Aqueous inkjet ink and ink sets

ABSTRACT

Aqueous inkjet ink compositions are useful in inkjet printing processes and can be used individually or as part of an inkjet ink set. Each aqueous inkjet ink composition has a dynamic viscosity of 5 centipoise (5 mPa-sec) or less at 25° C., and consists essentially of: (a) a polymer-dispersed pigment colorant at 0.9-6 weight %; (b) a composition consisting of compounds represented by the following Structure (I): 
       HO—CH 2 —CH 2 —R   (I)
 
     wherein R is a substituted or unsubstituted phenyl group or a substituted or unsubstituted phenoxy group, at 0.5-2 weight %; (c) a water-soluble humectant, co-solvent, or both, at than or equal to 20 weight %. Each polymer-dispersed pigment colorant has a 50 th  percentile particle diameter of less than 70 nm and a 95 th  percentile particle diameter of less than 150 nm, as measured using a dynamic light scattering particle size analyzer.

REFERENCED APPLICATIONS

Reference is made to the following copending patent applications, thedisclosures of all of which are incorporated herein by reference:

U.S. Ser. No. 16/______ filed on even date herewith by Cook andSowinski, and entitled “Aqueous Fluid Sets for Inkjet Printing Methods”(Eastman Kodak Attorney Docket K002252/JLT);

U.S. Ser. No. 16/______ filed on even date herewith by Sowinski, Cook,and Bugner, and entitled “Methods of Inkjet Printing” (Eastman KodakAttorney Docket K002253/JLT); and

U.S. Ser. No. 16/______ filed on even date herewith by Maldonado,Sowinski, Cook, and Bugner, and entitled “Absorbent Article withGraphics Printed in Preservative-free Ink, and Methods of ManufactureThereof” (Procter and Gamble Attorney Docket 15374).

FIELD OF THE INVENTION

This invention relates to aqueous inkjet ink compositions and inkjet inksets that can be used in inkjet printing processes such as continuousinkjet printing process. The inventive aqueous inkjet ink compositionscontain a unique set of preservatives that inhibit the growth ofmicroorganisms.

BACKGROUND OF THE INVENTION

The inkjet printing of substrates intended for direct contact with foodor skin requires careful consideration of the toxicity and the potentialfor unintended side effects from human exposure to the chemicalscontained in the inkjet inks. The most toxic chemicals in aqueous inkjetink compositions tend to be the industrial biocides used to preventmicrobial growth of bacteria, yeasts, and molds to extend compositionshelf-life. Isothiazolinones and formaldehyde released from precursorsor donors, for example, are generally safe and have high antimicrobialefficacy within their prescribed usage levels. Nonetheless, suchcompounds have been recently found objectionable in certain productsintended for skin contact because sensitive users can experience skinirritation and dermatitis following exposure to even trace levels.Regulatory bodies and advocacy groups are becoming more influential inwhat chemicals are used in such consumer products. In addition, thepopulation of consumers is becoming more aware of the use of commonpreservatives in various products and are developing a preference forproducts that do not contain them.

A need remains to provide alternative preservatives (or biostats andbiocides) with a record of safety and acceptance in skin contactapplications that are effective at suppressing microbial contaminantgrowth in aqueous inkjet ink compositions without destabilizing pigmentor dye-based colorants or compromising the high-quality printing processin some other fashion.

Piezoelectric drop-on-demand (DOD) inkjet inks are disclosed in U.S.Patent Application Publication 2017/0073535A1 (Kusukame et al.) usingselections of conventional and unconventional components.

The use of 2-phenoxyethanol (identified as ethylene glycol phenyl ether)in continuous inkjet printing (CIJ) processes using aqueous dye-basedand pigment-based inks is disclosed in U.S. Pat. No. 6,071,334 (Wider etal.).

Ethylene glycol phenyl ether is described as a substantially waterinsoluble oil at about 3 weight % in thermal DOD black inkjet inkscomprised of self-dispersed carbon black pigments, as disclosed in U.S.Pat. No. 5,749,952 (Tsang et al.)

Pigmented thermal DOD inkjet ink compositions using self-dispersed blackpigment and acrylate polymer binder experience reduced “deceleration”(loss of drop velocity during periods of extended nozzle firing) if adeceleration-alleviating component selected from a group of materialsincluding ethylene glycol phenyl ether is incorporated in the ink asdescribed in U.S. Pat. No. 6,726,757B2 (Sarkisian et al.).

The use of 2-phenylethanol (identified as β-phenylethyl alcohol) in afragrant aqueous inkjet ink composition intended to impart rose scent isdisclosed in U.S. Pat. No. 6,123,757 (Yang et al.).

Despite these various innovations, there is an unmet need for aqueousinkjet ink compositions and particle-free fluids that are substantiallyfree of common preservatives or biocides, while preserving desiredcontinuous inkjet printing (CIJ) features and high-quality images.

SUMMARY OF THE INVENTION

The present invention provides an aqueous inkjet ink composition havinga dynamic viscosity of less than or equal to 5 centipoise (5 mPa-sec) at25° C. as measured using a rolling ball viscometer, and consistingessentially of:

(a) one or more polymer-dispersed pigment colorants in a total amount ofat least 0.9 weight % and up to and including 6 weight %, based on thetotal weight of the aqueous inkjet ink composition;

(b) a composition consisting of one or more compounds represented by thefollowing Structure (I):

HO—CH₂—CH₂—R   (I)

wherein R is a substituted or unsubstituted phenyl group or asubstituted or unsubstituted phenoxy group, in a total amount of atleast 0.5 weight % and up to and including 2 weight %, based on thetotal weight of the aqueous inkjet ink composition;

(c) one or more compounds selected from water-soluble humectants,co-solvents, and both water-soluble humectants and co-solvents, in anamount of less than or equal to 20 weight %, based on the total weightof the aqueous inkjet composition,

wherein each of the one or more polymer-dispersed pigment colorants hasa 50^(th) percentile particle diameter of less than 70 nm and a 95^(th)percentile particle diameter of less than 150 nm, all particle diametersbeing measured using a dynamic light scattering particle size analyzer.

This invention also provides an ink set comprising two or more aqueousinkjet ink compositions, each of which independently has a dynamicviscosity of less than or equal to 5 centipoise (5 mPa-sec) at 25° C.,and each of which aqueous inkjet ink compositions independently consistsessentially of:

(a) one or more polymer-dispersed pigment colorants in a total amount ofat least 0.9 weight % and up to and including 6 weight %, based on thetotal weight of the aqueous inkjet ink composition;

(b) a composition consisting of one or more compounds represented by thefollowing Structure (I):

HO—CH₂—CH₂—R   (I)

wherein R is a substituted or unsubstituted phenyl group or asubstituted or unsubstituted phenoxy group, in a total amount of atleast 0.5 weight % and up to and including 2 weight %, based on thetotal weight of the aqueous inkjet ink composition;

(c) one or more compounds selected from water-soluble humectants,co-solvents, and a combination of water-soluble humectants andco-solvents, in an amount of less than or equal to 20 weight %, based onthe total weight of the aqueous inkjet composition,

wherein each of the one or more polymer-dispersed pigment colorants hasa 50^(th) percentile particle diameter of less than or equal to 70 nmand a 95^(th) percentile particle diameter of less than or equal to 150nm, all particle diameters being measured using a dynamic lightscattering particle size analyzer.

The stable aqueous pigment dispersions and inkjet ink compositionsaccording to the present invention exhibit improved resistance tomicrobial growth and are acceptable for skin contact because of thepresence of 2-phenoxyethanol, 2-phenylethanol, or a combination thereofwhen commonly used industrial biocidic preservatives such asisothiazolinone derivatives and formaldehyde releasers are withheld fromsuch formulations. Used individually or in combination, these ethanolderivatives were effective at suppressing the growth of a representativemixture of gram-negative and gram-positive bacteria during in vitrochallenge testing of the inkjet ink compositions. Combined withappropriate supplemental antimicrobial compounds, susceptibility togrowth of a very broad array of microbial organisms in the compositionscan be satisfactorily minimized during extended challenge testing. Amethod of continuous inkjet (CIJ) printing is provided according to thepresent invention when the aqueous inkjet ink compositions are used andreplenished in the CIJ printer fluid system for recirculating ink usingan aqueous particle-free fluid containing 2-phenoxyethanol,2-phenylethanol, or other alternative preservatives. The printedsubstrates obtained according to the present invention can be porousmatted media (for example, paper), woven media (for example, a textile),and porous or non-porous films (for example, a polymer sheet) that canbe pre-treated or pre-coated to better receive and bind the printedinkjet inks to the printed media or article.

Further details and advantages of the present invention can beunderstood from the teaching provided below.

DETAILED DESCRIPTION OF THE INVENTION

The following discussion is directed to various embodiments of thepresent invention and while some embodiments can be desirable forspecific uses, the disclosed embodiments should not be interpreted orotherwise considered to limit the scope of the present invention, asclaimed below. In addition, one skilled in the art will understand thatthe following disclosure has broader application than is explicitlydescribed in the discussion of any embodiment.

Definitions

As used herein to define various components of the aqueous organicpigment dispersions, aqueous inkjet ink compositions, and othermaterials used in the practice of this invention, unless otherwiseindicated, the singular forms “a,” “an,” and “the” are intended toinclude one or more of the components (that is, including pluralityreferents).

Each term that is not explicitly defined in the present application isto be understood to have a meaning that is commonly accepted by thoseskilled in the art. If the construction of a term would render itmeaningless or essentially meaningless in its context, the term shouldbe interpreted to have a standard dictionary meaning.

The use of numerical values in the various ranges specified herein,unless otherwise expressly indicated otherwise, are considered to beapproximations as though the minimum and maximum values within thestated ranges were both preceded by the word “about”. In this manner,slight variations above and below the stated ranges may be useful toachieve substantially the same results as the values within the ranges.In addition, the disclosure of these ranges is intended as a continuousrange including every value between the minimum and maximum values aswell as the end points of the ranges.

As used herein, the parameter “acid number” (also known as acid value)is defined as the milligrams (mg) of potassium hydroxide required toneutralize 1 g of an acidic polymer.

The term “aqueous” in aqueous organic pigment dispersions, and aqueousinkjet ink compositions, according to the present invention means thatthe water content is greater than 60 weight % based on the total amountof solvents. Thus, water is the predominant solvent in the aqueousmedium.

Ink and fluid dynamic viscosity can be measured by any of well-knowntechniques. Preferred methods include measurement of the timing of massflow through a capillary as in a capillary viscometer, or measurement ofball drop velocity through a fluid, using for example a rolling ballviscometer. Both a capillary flow viscometer and a commerciallyavailable Anton Paar Automated MicroViscometer (AMVn) employing therolling ball technique can be used to measure the dynamic viscositiesreported herein. All ink dynamic viscosity values disclosed herein weremeasured under gravity induced shear at approximately 24° C. to 26° C.It will be appreciated that the values cited are reported as centipoise(cP) or milliPascal seconds (mPa-sec) and that 1 cP=10⁻³ Pascal-seconds(Pa-s)=10⁻² dyne-s/cm². While viscosities can be measured with highprecision, viscosity values here are reported to one or two decimalplaces only, and they are normally rounded values and not truncatedvalues. All claims reciting ink viscosities are intended to beinterpreted in terms of values in mPa-sec normally rounded to onedecimal point. Thus, the various aqueous inkjet ink compositions canhave a viscosity of up to and including 10 centipoise (10 mPa-sec).

The Wilhelmy plate method is a well-known technique for measuring thestatic surface tension of a liquid ink or service fluid at a solidinterface. The technique involves a plate of known dimensions, typicallyselected from a roughened platinum alloy, suspended from a balance. Theplate is contacted with a solution of interest and a vertical force isapplied to the plate to form a liquid meniscus between the solution andplate. The resulting surface tension is given according to equation (1):

σ=F/L cos(θ)  (1)

where σ is the surface tension of the liquid, F is the force acting onthe balance (milli-Newtons/meter), L is the wetted length of the platein millimeters, and θ is the contact angle between the plate andsolution.

Typically, the roughened platinum results in a contact angle very closeto zero and the cosine of θ goes to 1. A complete theoretical treatmentof the method can be found in, for example, “A Method for DeterminingSurface and Interfacial Tension Using a Wilhelmy Plate,” Colloid andPolymer Science, 255 (7), pages 675-681. A number of commerciallyavailable instruments are known for measuring surface tension, however,the instrument used to report surface tension values in the presentinvention is a Krüss Model K10ST tensiometer.

The pigment colorants used in the various embodiments of the presentinvention are not generally self-dispersing meaning that they requirethe presence of one or more organic polymeric pigment dispersants boundto some fraction of the surface of the pigment particles to keep themsuspended in an aqueous medium.

The terms “water-soluble” and “aqueous-soluble” mean that 1 mass part ofsolute material can be dissolved in as little as less than 1 mass part(i.e., more soluble solute) and in as much as 1,000 mass parts (that is,less soluble solute) of distilled water at 25° C. to provide ahomogeneous and visibly clear solution.

The term “solvo-surfactant” refers to a compound or combination ofcompounds that are effective solvents for dried “ink,” and are volatilesolvents having a boiling point at sea level of less than 200° C. andcapable of reducing fluid surface tension and self-aggregating. Furtherdetails of such compounds are provided below.

For clarification of definitions for any terms relating to polymers,reference should be made to “Glossary of Basic Terms in Polymer Science”as published by the International Union of Pure and Applied Chemistry(“IUPAC”), Pure Appl. Chem. 68, 2287-2311 (1996). However, anydefinitions explicitly set forth herein should be regarded ascontrolling. Polymers can be prepared from ethylenically unsaturatedpolymerizable monomers using free radical polymerization or acidcatalyzed polymerization processes, or by reaction of appropriatecondensation monomers (for example diols and diisocyanates) using knowncondensation polymerization processes.

Unless otherwise indicated, the terms “polymer” and “polymeric” refer toboth homopolymers and copolymers, each having a stated weightdistribution average molecular weight (M_(w)) or a number distributionaverage molecular weight (M_(n)) as measured using gel permeationchromatography (polystyrene standard).

The term “copolymer” refers to polymers that are derived from two ormore different monomers, in random order or a predetermined order (forexample, block) along the polymer backbone. That is, each copolymercomprises at least two recurring units having different chemicalstructures.

The term “backbone” refers to the chain of atoms in a polymer to which aplurality of pendant groups can be attached. An example of such abackbone is an “all carbon” backbone obtained from the polymerization ofone or more ethylenically unsaturated polymerizable monomers. However,other backbones can include heteroatoms wherein the polymer is formed bya condensation reaction or some other means.

Aqueous Organic Pigment Dispersions

(a) Polymer dispersed pigment colorants useful in the practice of thisinvention can be used singly, or in combinations of two or moredifferent polymer-dispersed pigment colorants, to provide any desiredcolor or hue. For example, a polymer-dispersed carbon black pigment canbe combined with a different polymer-dispersed colored organic pigmentin the same aqueous pigment dispersion or aqueous inkjet inkcomposition. The exact choice of polymer-dispersed pigment colorantswill depend upon the specific application, performance, colorreproduction, and image stability that are desired. Usefulpolymer-dispersed pigment colorants are described for example in U.S.Pat. No. 5,026,427 (Mitchell et al.), U.S. Pat. No. 5,141,556 (Matrick),U.S. Pat. No. 5,160,370 (Suga et al.), and U.S. Pat. No. 5,169,436(Matrick), the disclosures of all of which are incorporated herein byreference.

Useful pigment colorants that can be dispersed with organic polymersinclude but are not limited to, azo pigments, monoazo pigments, disazopigments, azo pigment lakes, β-naphthol pigments, naphthol AS pigments,benzimidazolone pigments, disazo condensation pigments, metal complexpigments, isoindolinone and isoindoline pigments, quinacridone pigments,polycyclic pigments, phthalocyanine pigments, perylene and perinonepigments, thioindigo pigments, anthrapyrimidone pigments, flavanthronepigments, anthanthrone pigments, dioxazine pigments, triarylcarboniumpigments, quinophthalone pigments, diketopyrrolo pyrrole pigments,titanium dioxide, iron oxide, and carbon blacks. Representative usefulyellow, black, green, brown, red, magenta, cyan, blue, orange, andviolet pigment colorants are described in Col. 7 (line 48) to Col. 8(line 5) of U.S. Pat. No. 8,173,215 (Sowinski et al.), the disclosure ofwhich is incorporated herein by reference.

Useful pigment colorants can be accompanied or dispersed using suitablepolymer dispersants that are well known in the art (as cited above).Representative useful organic polymer dispersants can be prepared fromat least one anionic hydrophilic monomer such as an acrylic acid ormethacrylic acid monomer, or combinations thereof, and for example, atleast one monomer comprised of a hydrophobic methacrylate or acrylatemonomer having an aliphatic chain having 12 or more carbon atoms, asdescribed for example in U.S. Patent Application Publication2007/0043144 (House et al.), the disclosure of which is incorporatedherein by reference. Further details of useful organic polymerdispersants, including useful monomer recurring units, monomer amounts,and M_(w), are provided in Col. 5 (line 45) to Col. 6 (line 31) of U.S.Pat. No. 8,173,215 (noted above).

Many useful organic polymer dispersants are anionic acrylic polymersformed from at least one anionic hydrophilic monomer described abovehaving a weight average (M_(w)) molecular weight of at least 500 Daltonsbut less than 100,000 Daltons, and more likely up to and including15,000 Daltons, or up to and including 10,000 Daltons.

One or more organic polymer dispersants for the pigment colorants can bepresent in an amount that would be readily apparent to one skilled inthe art depending upon the aqueous medium, the chosen organic pigments,and other components of the aqueous inkjet ink composition.

In addition to the polymeric dispersants, nonionic or anionicsurfactants can be present with the pigment colorants as is known in theart. Representative materials of this type include but are not limitedto, sodium dodecylsulfate or sodium oleylmethyltaurate as described forexample in Col. 7 (lines 15-23) of U.S. Pat. No. 8,173,215 (notedabove).

Particle sizes for each useful polymer-dispersed pigment colorants areas follows.

Particle size for the various polymer-dispersed pigment colorants refersto the approximate diameter of a generally spherical pigment particle orto the approximate largest characteristic dimension of a non-sphericalparticle. More particularly, the diameter of a sphere having the samevolume as the particle is determined in practice (that is, equivalentsphere diameter). The desired median particle diameter (or 50^(th)percentile particle diameter) of each of the pigmented colorants usedaccording to this invention can be less than 300 nm, less than 150 nm,less than 70 nm, or even less than 60 nm, such that 50% of the volume ofthe particles is composed of particles having diameters smaller than theindicated diameter. In addition, at least 95% of the total primaryparticles of each polymer-dispersed pigment colorant used according tothis invention have a particle diameter of less than 500 nm, less than300 nm, less than 150 nm, or even less than 110 nm. This refers to the95^(th) percentile particle diameter that is the classified particlesize distribution such that 95% of the volume of organic pigmentparticles is provided by particles having diameters smaller than theindicated diameter. Particle size (or particle volume) can be readilymeasured using a conventional dynamic laser light scattering particlesize analyzer. Instrumental techniques for analyzing and reportingnanoparticle sizes are usefully described in “Particle SizeCharacterization”, published by the National Institute of Standards andTechnology (“NIST”), Special Publication 960-1, 93-139 (2001).

The (b) composition used in the practice of this invention consists ofone or more compounds represented by the following Structure (I):

HO—CH₂—CH₂—R   (I)

wherein R is a substituted or unsubstituted phenyl group or asubstituted or unsubstituted phenoxy group. For example, R can be eitheran unsubstituted phenyl group or an unsubstituted phenoxy group.Mixtures of compounds represented by Structure (I) can also be used.

Thus, either or both of 2-phenoxyethanol and 2-phenylethanol can be usedto advantage in the practice of this invention for the advantagesdescribed above. 2-Phenoxyethanol is also known as ethylene glycolphenyl ether; ethylene glycol monophenyl ether; and1-hydroxy-2-phenoxyethane, and can be obtained as DOWANOL PhE, DOWANOLEPh, or DOWANOL EP from various commercial sources. 2-Phenylethanol isalso known as phenylethanol; 2-phenylethan-1-ol; phenethyl alcohol;β-hydroxyethylbenzene; phenylethyl alcohol; β-phenylethanol; and benzylcarbinol and can be obtained from various commercial sources.

An aqueous medium such as water and any water-miscible organic solvents,can be present in any desirable amount that would provide desiredviscosity and other physical properties for storage or use of an aqueouspigment dispersion to make aqueous inkjet ink compositions.

An aqueous pigment dispersion according to this invention can beprepared by any method commonly used in the art, and typically involvestwo steps: (a) a dispersing or milling step to break up aggregates ofone or more pigment colorants into primary particles wherein a primaryparticle is defined as the smallest identifiable subdivision in aparticulate system; and (b) a dilution step in which the pigmentcolorant dispersion from step (a) is diluted by addition of aqueousmedium and any other additives. Milling details are described forexample in Col. 6 (line 58) to Col. 7 (23) of U.S. Pat. No. 8,173,215(noted above).

Aqueous Inkjet Ink Compositions

The aqueous inkjet ink compositions according to the present inventiongenerally have a dynamic viscosity that is generally less than or equalto 5 centipoise (5 mPa-sec), or at least 1 centipoise (1 mPa-sec) and upto and including 3 centipoise (3 mPa-sec), all measured at 25° C. usinga rolling ball viscometer, or a capillary viscometer, and knownprocedures.

The aqueous inkjet ink compositions also typically have a pH of at least7.5 and up to and including 11, or more likely of at least 8 and up toand including 9. When the aqueous inkjet ink composition is used inhardware with nickel or nickel-plated apparatus components, a corrosioninhibitor such as the sodium salt of 2- or 5-methyl-1-H-benzotriazolecan be added, and the pH can be adjusted to at least 10 and up to andincluding 11. If printheads fashioned out of silicon are used for inkjetprinting, the aqueous inkjet ink composition pH can be adjusted to atleast 7.5 and up to and including 10, or at least 8 and up to andincluding 9.5.

Aqueous inkjet ink compositions according to the present inventioncomprise one or more (a) polymer-dispersed pigment colorants in a totalamount of at least 0.9 weight % and up to and including 6 weight %, orat least 1.5 weight % and up to and including 5 weight %, based on thetotal weight of the aqueous inkjet ink composition. Usefulpolymer-dispersed pigment colorants, and useful particle sizeparameters, are described above. Two or more polymer-dispersed pigmentcolorants can be used if desired to provide a desired hue or color inthe resulting inkjet-printed image.

The (b) composition described above consisting of one or more compoundsrepresented by Structure (I) is present in the aqueous inkjet inkcompositions, in a total amount of at least 0.5 weight % and up to andincluding 2 weight %, or even at least 1 weight % and up to andincluding 1.8 weight %, based on the total weight of the aqueous inkjetink composition.

Each aqueous inkjet ink composition according to the present inventioncomprises (c) one or more compounds selected from water-solublehumectants, co-solvents, and both water-soluble humectants andco-solvents. The co-solvents are generally water-soluble orwater-miscible organic solvents having a viscosity that is greater than1 centipoise (1 mPa-sec) and that can exceed even 40 centipoise (40mPa-sec) when measured at 25° C. using a standard rolling ball,capillary, or spinning plate viscometer. Any water-soluble humectant orco-solvent known in the inkjet art that is compatible with the otherrequirements of the invention can be used. While an individual humectantcan be employed, mixtures of two or more humectants, each of whichimparts a useful property, can be used. Representative humectants aredescribed for example, in U.S. Pat. No. 9,828,513 (Lussier et al.), thedisclosure of which is incorporated herein by reference, and includeclasses of compounds such as (1) mono-alcohols; (2) polyhydric alcohols;(3) lower mono- and di-alkyl ethers derived from a polyhydric alcohol;(4) nitrogen-containing compounds such as urea, 2-pyrrolidone,N-methyl-2-pyrrolidone, and 1,3-dimethyl-2-imidazolidinone; and (5)sulfur-containing compounds such as 2,2′-thiodiethanol, dimethylsulfoxide, and tetramethylene sulfone. Useful co-solvents are alsoincluded within such classes of compounds.

The one or more (c) humectants, co-solvents, or both humectants andco-solvents can be present in an amount of less than 20 weight %, or atleast 0.5 weight %, or at least 1 weight % and up to and including 15weight %, or at least 3 weight % and up to and including 10 weight %,all based on the total weight of the aqueous inkjet ink composition.Highly preferred levels of the one or more (c) humectants, co-solvents,or both humectants and co-solvents are at least 4 weight % and up to 8weight %.

One or more (d) supplemental antimicrobial agents can also be present inthe aqueous inkjet ink compositions, and such materials are differentfrom the (b) composition described above and represented by Structure(I). Representative materials include but are not limited to,iodopropynyl butyl carbamate (CAS 55406-53-6), piroctone olamine (CAS68890-66-4), 2,4-dichlorobenzyl alcohol (CAS 1777-82-8), boric acid (CAS10043-35-3) and monovalent and divalent metal ion salts derived fromboric acid, and combinations of these materials. A useful amount of theone or more supplemental antimicrobial agents is at least 0.01 weight %and up to and including 3 weight %, based on the total weight of theaqueous inkjet ink composition.

Each aqueous inkjet ink composition according to the present inventioncan further comprise one or more anionic polyurethanes, each having anacid number of at least 50, or of at least 60 and up to and including150, or even at least 55 and up to and including 90, which acidicpolymers are described in more detail below.

Alternatively, or in addition to the anionic polyurethanes, the aqueousinkjet ink composition can comprise one or more anionic non-aromaticacrylic or anionic styrene-acrylic polymers, each having an acid numberof at least 50, or of at least 120 and up to and including 240, or evenat least 160 and up to and including 220, which acidic polymers aredescribed in more detail below. Mixtures of two or more of suchmaterials can be used if desired.

Representative examples of both types of anionic polymers are describedfor example in U.S. Pat. No. 8,430,492 (Falkner et al.) the disclosureof which is incorporated herein by reference, and in U.S. Pat. No.9,783,553 (noted above). Particularly useful anionic polyurethanescontain a polyether diol unit and can be identified as polyetherpolyurethanes. Such anionic polyether polyurethanes generally can have amolecular weight (M_(w)) of at least 10,000 Daltons and up to andincluding 30,000 Daltons or at least 15,000 Daltons and up to andincluding 25,000 Daltons. For example, particularly useful polyetherpolyurethanes are individually represented by Structure (I) in U.S. Pat.No. 9,783,553 (noted above).

Useful water-soluble or water-dispersible anionic polyetherpolyurethanes can be prepared as described for example in [0045]-[0049]of U.S. Patent Application Publication 2008/0207811 (Brust et al.), thedisclosure of which is incorporated herein by reference. The acidicgroups in the anionic polyether polyurethanes can be at least partiallyand up to 100% neutralized (converted into salts) using monovalentinorganic bases such as alkaline metal hydroxides or organic amines suchas dimethylethanolamine.

Representative anionic non-aromatic acrylic polymers and anionicstyrene-acrylic polymers useful in the present invention are alsodescribed for example in [0061] of U.S. Patent Application Publication2008/207811 (noted above). Examples of useful anionic styrene-acrylicpolymers include those commercially available under the trademarksJONCRYL® (BASF Corp.), TRUDOT® (formerly available from Mead WestvacoCo.), and VANCRYL® (Allnex USA, Inc.).

The useful amounts of such anionic polymers are readily known in the artand can be up to and including 15 weight %, or up to and including 10weight %, all based on the total weight of the aqueous inkjet inkcomposition. Particularly useful amounts of anionic polymers range areat least 1 weight % and up to and including 5 weight %, includinganionic non-aromatic acrylic polymers and anionic styrene-acrylicpolymers used as the pigment dispersant.

In addition, modified polysiloxanes can be present in the aqueous inkjetinks compositions. Examples of such materials include ethoxylated orpropoxylated silicone-based “surfactants” that can be obtainedcommercially under the trademarks SILWET® (CL Witco), and BYK® (BykChemie) such as BYK® 348 and 381, as well as Dow Corning DC67, DC57,DC28, DC500W, and DC51. Non-silicone surfactants can also be used,including but not limited to anionic, cationic, nonionic, or amphotericsurfactants such as those commercially available as SURFYNOL®surfactants (Evonik Corp.) including SURFYNOL® 440 and 465 alkynediolsurfactants. Useful amounts of such materials are readily apparent toone skilled in the art. Particularly useful amounts of selectedsurfactants are described in U.S. Pat. No. 8,455,570B2 (Lindstrom etal.), the disclosure of which is herein incorporated by reference.

It can be useful to include one or more “promoters” in the aqueousinkjet ink compositions potentially to enhance the effectiveness of thecompounds represented by Structure (I) in the (b) composition. Suchmaterials are generally alkane diols, each having at least 7 carbonatoms and up to and including 12 carbon atoms, and particularly havingat least 7 carbon atoms and up to and including 10 carbon atoms.Representative useful compounds that can be used singly or incombination as promoters include but are not limited to,1,7-heptanediol, 1,2-heptandiol, 2-ethyl-1,3-hexanediol, 1,2-octandiol,3,6-octanediol, 2,2,4-trimethyl-1,3-pentandiol, 1,2-nonanediol,1,10-decanediol, 1,12-dodecanediol, and others that would be readilyapparent to one skilled in the art. 1,2-Octanediol is particularlyuseful in this regard.

One or more promoters can be present in the aqueous inkjet inkcompositions at a total amount of less than or equal to 1.5 weight % orless than or equal to 1.25 weight %, based on the total weight of theaqueous inkjet ink composition. A minimum amount can be at least 0.3weight %.

Colorless fluorescent colorants (dyes or pigments) can also be presentin the aqueous inkjet ink compositions in amounts readily apparent toone skilled in the art, and examples of such compounds are described inU.S. Patent Application Publication 2014/231674 (Cook), the disclosureof which is incorporated herein by reference.

Other additives that can be present in the aqueous inkjet inkcompositions, in amounts that would be readily apparent to one skilledin the art, include but are not limited to: surfactants besides thosedescribed above to adjust composition surface tension, including but notlimited to the TERGITOL® 15-S and TMN series nonionic surfactants, BRIJ®series nonionic surfactants; TRITON® series nonionic surfactants, ZONYL®fluoro surfactants; PLURONIC® nonionic surfactants; TETRONIC® nonionicsurfactants, SILWET® nonionic surfactants, and SURFYNOL® nonionicsurfactants, and various anionic and cationic surfactants mentioned inCol. 10, line 64 to Col. 11, line 14 of U.S. Pat. No. 8,173,215 (notedabove)]; thickeners; conductivity-enhancing agents; drying agents;waterfast agents; viscosity modifiers; pH buffers; antifoamants; wettingagents; corrosion inhibitors; antifoamants and defoamers (such asSURFYNOL® DF-110L, PC, MD-20, and DF-70); UV radiation absorbers;antioxidants; and light stabilizers available under the trademarksTINUVIN® (BASF Corp.) and IRGANOX® (BASF Corp.), as well as otheradditives described in Col. 17 (lines 11-36) of U.S. Pat. No. 8,455,570(noted above). The useful amounts of such materials would be readilyapparent to one skilled in the art using routine experimentation.

Water is generally present in each aqueous inkjet ink as the primaryaqueous medium, in a suitable amount such as at least 75 weight % or atleast 80 weight %, and generally at no more than 90 weight %, based onthe total weight of the aqueous inkjet ink composition.

Each aqueous inkjet ink composition described herein can be prepared bydispersing suitable polymer-dispersed pigments colorants in water andmixing in other noted materials such as the (b) compounds represented byStructure (I), (c) humectants or co-solvents, and any adjuvants,promoters, supplemental antimicrobial agents, and additional materialsin suitable amounts.

Ink Sets

Ink sets can be provided by the present invention, and they can includetwo or more aqueous inkjet ink compositions, each of which comprises atleast one visible polymer-dispersed pigment colorant (described above)to provide a desired color or hue. For example, each ink set can includeuseful aqueous inkjet ink compositions which can have different hues or“colors” such as various shades of orange, red, violet, green, cyan,yellow, black, magenta, brown, pink, and blue and thus contain one ormore suitable polymer-dispersed pigment colorants suitable to providethe desired hue. Any desirable hue, for example as defined using knowna* and b* CIELAB values, can be provided by proper use and formulationof suitable polymer-dispersed pigment colorants. Aqueous “white” inkjetink compositions are also useful in certain situations and can beincluded in an ink set. A wide variety of organic and inorganic pigmentscan be used individually or in combination in such aqueous inkjet inkcompositions, as described above, and they can have the desired pigmentparticle size as described above. The polymer-dispersed pigmentcolorants can be present in suitable amounts as described above for theaqueous inkjet ink compositions according to this invention

In addition to the polymer-dispersed pigment colorants, one or more ofthe aqueous color inkjet ink compositions in an ink set can include oneor more aqueous-soluble dyes that are well known in the art, for exampleas described in Col. 12 (lines 4-55) of U.S. Pat. No. 8,455,570 (notedabove).

The aqueous inkjet ink compositions in the ink sets can be formulatedthe same as or differently from those described above.

Each aqueous color inkjet ink compositions in an ink set can have adesirable pH of at least 7.5 and up to and including 11, or at least 8and up to and including 10, as described above using suitable bases andbuffer systems.

In addition, each aqueous color inkjet ink composition can have suitabledynamic viscosity of at least 1 centipoise (1 mPa-sec) but less than 5centipoise (5 mPa-sec) as measured at 25° C.

Each of the aqueous inkjet ink compositions in an ink set independentlycomprises (has same or different): (a) a polymer-dispersed pigmentcolorant (as described above) in an amount of at least 0.9 weight % andup to and including 6 weight %, based on the total weight of the aqueousinkjet ink composition; a (b) composition consisting of compoundsrepresented by Structure (I) as described above; and (c) at least onewater-soluble humectant, co-solvent, or a combination of water-solublehumectant and co-solvent, all as described above and in the amountsdescribed above.

For example, an ink set according to the present invention can have twoor more of the following specific types of aqueous inkjet inkcompositions:

(i) an aqueous inkjet ink composition comprising a polymer-dispersedcyan pigment colorant,

(ii) an aqueous inkjet ink composition comprising a polymer-dispersedmagenta pigment colorant,

(iii) an aqueous inkjet ink composition comprising a polymer-dispersedyellow pigment colorant, and

(iv) an aqueous inkjet ink composition comprising a polymer-dispersedblack pigment colorant.

In many ink sets, all four (i) through (iv) aqueous inkjet inkcompositions are present.

In some embodiments, an ink set according to this invention can furthercomprise a particle-free colorless inkjet composition (or aqueousparticle-free fluid), for example as described in U.S. Pat. No.8,764,161 (noted above), the disclosure of which is incorporated hereinby reference. Such compositions can be known as “fluids” in the art andcan have various purposes or functions such as printhead maintenance,storage, flushing, or cleaning, or use as replenishment fluids. Thedetails of such fluids are provided in the cited patent, the disclosureof which is incorporated herein by reference. By “particle-free,” it ismeant that such compositions do not purposely contain particulates orpigments of any type, colorless or colored. Further details of usefulsuch fluids are provided below in the discussion of individual aqueousparticle-free “fluid sets.”

Such particle-free colorless inkjet compositions can also comprise a (b)composition consisting of compounds represented by Structure (I)described above, which compounds can be the same as or different fromthose used in the two or more aqueous inkjet ink compositions in an inkset containing a polymer-dispersed pigment colorant. For example, suchparticle-free colorless inkjet compositions can contain2-phenoxyethanol, 2-phenylethanol, or both 2-phenoxyethanol and2-phenylethanol [as when R is 2-phenyl or 2-phenoxy in Structure (I)] inan amount of at least 0.5 weight % and up to and including 2 weight %,based on the total weight of the particle-free colorless inkjetcomposition.

The durability, gloss, and other properties of an inkjet printed imagecan be improved by the application of a colorless polymeric overcoatcomposition, which can be considered an aqueous particle-free inkjetcomposition according to this invention. Examples of such compositionsare provided in U.S. Pat. No. 7,219,989 (Uerz et al.). In other toachieve high inkjet printing speeds and throughput associated with CIJprinting, such an overcoat composition can be applied using a CIJprinthead following in-line with one or more printheads of drop-formingnozzles dispensing “colored” aqueous inkjet ink compositions. Furtherdetails about such application are provided in Col. 17 (lines 16-48) ofU.S. Pat. No. 8,173,215 (noted above).

Additional aqueous particle-free inkjet compositions (or inks) that canbe part of an ink set include those described in U.S. Patent ApplicationPublication 2018/0051184 (Lussier et al.) that can be inkjet printed toprovide colorless or colored coatings, the disclosure of whichpublication is incorporated herein by reference. Such compositions cancomprise at the least, one or more anionic polyether polyurethanes oranionic acrylic or styrene-acrylic polymers as described above, as wellas a suitable antifoamant or defoamer to reducing foaming propensities.Such aqueous particle-free inkjet compositions can further comprise a(b) composition having compounds defined by Structure (I) as describedabove.

Each component or composition present in an ink set, whether colored orcolorless, may contain various other additives (such as defoamers,surfactants, conductivity enhancing agents, drying agents, water-fastagents, chelating agents, thickeners, anti-kogation agents, stabilizers,and buffering agents) that would be readily apparent to one skilled inthe art.

Aqueous Particle-Free Fluids

Aqueous particle-free fluids can be designed and used in the practice ofthe present invention for various purposes. Each of these aqueousparticle-free fluids generally independently has a dynamic viscosity ofless than or equal to 5 centipoise (5 mPa-sec) at 25° C. for example asmeasured using a rolling ball viscometer, or a capillary viscometer, andstandard procedures. Each of these aqueous particle-free fluidspurposely contains no particles, colorless or otherwise, and can be usedfor various purposes or functions in inkjet printing methods, asdescribed below.

Two or more of such aqueous particle-free fluids, having the same ordifferent purposes, can be incorporated into a “fluid set” forcommercialization if desired. Alternatively, one or more of the aqueousparticle-free fluids can be included within the ink sets describedabove.

Each aqueous particle-free fluid independently can have a pH broadlysimilar to the aqueous inkjet ink compositions described above, that is,of at least 5 and up to and including 11. pH can be managed for eachaqueous particle-free fluid using the teaching in Col. 11 (line 58) toCol. 12 (line 26) of U.S. Pat. No. 8,764,161 (noted above). In someembodiments, the pH is at least 10 and up to and including 11 and can bemanaged by the presence of one or more bases, as described below.

Each of the aqueous particle-free fluids according to the presentinvention independently consists essentially of a (b) compositionconsisting of one or more compounds represented by Structure (I) asdefined above. Individual aqueous particle-free fluids in a fluid setcan have the same or different (b) composition. The one or morecompounds in the (b) composition, for example those wherein R is2-phenyl or 2-phenoxy, can be present in an aqueous particle-free fluidin an amount of at least 0.5 weight % and up to and including 2 weight%, based on the total weight of the aqueous particle-free fluid.

In a particular embodiment, the aqueous particle-free fluids can havedifferent general compositions aside from their (b) composition and aresuitable for two or more different printing service functions. Forexample, a “replenisher” aqueous particle-free fluid can be used torestore evaporated solvent from the aqueous inkjet ink composition inthe ink tank and return that composition to a previous colorantconcentration. Such aqueous particle-free fluids generally consistessentially of only the (b) composition described above. However, it ispossible for such aqueous particle-free fluids to additionally include ahumectant, co-solvent, supplemental antimicrobial agent, surfactant,promoter, or any combination thereof, as described in more detail below.For example, such aqueous particle-free fluids can desirably alsocontain any volatile organic solvents that are lost to evaporationduring ink recycling, or a weak organic base (for example, analkanolamine) to mitigate pH drift due to carbonic acid formationresulting from carbon dioxide uptake. Since a continuous inkjet printerfluid system method of determining the relative concentration of the inkin the ink tank is to measure the ink's ionic conductivity (oralternatively its resistivity), it is undesirable to alter the restoredink fluid properties and ion inventory materially with contributionsthat accumulate from repeated replenisher addition. Thus, it is desiredto minimize the replenisher aqueous particle-free fluid content of forexample, organic solvents, humectants, pH and ionic conductivitymodifying additives, polymer compounds, surfactants, and antifoamants.

A “maintenance” aqueous particle-free fluid, a printhead cleaner andstorage fluid, can be used to re-dissolve, re-disperse, or solubilizedried ink deposits that form on and around the nozzle plate nozzles andinterfere with inkjet straightness and inkjet stability. It can then beused to purge the printhead ink channels and external surfaces to flushink away. The aqueous particle-free fluid is also suitable for keepingthe wetted parts ready for efficient start-ups after periods of extendedstorage, but the various printhead and fluid system maintenancefunctions of flushing, cleaning, and storage can be accomplished byspecialized individual aqueous particle-free fluids as desired.

In addition to a (b) composition, a printhead cleaner and storageaqueous particle-free fluid according to the present invention candesirably be comprised of an organic solvent that improves upon theeffectiveness of the fluid vehicle (water) in penetrating and solvatingdried pigment particles in deposits of dried aqueous inkjet inkcomposition. It may additionally contain optional additives that includebut are not limited to a solubilizing agent, a co-solvent, viscositymodifiers, a base, an acid, a pH buffer, a chelating agent, adispersant, a water-soluble or water-dispersible polymer, a corrosioninhibitor, a viscosity modifier, a penetrant, a wetting agent, anantifoamant, and a defoamer. Effective solvents for dried aqueous inkjetink composition can be selected from the class of dynamic surfacetension reducing co-solvents also known in the art as penetrants, wherethe dynamic surface tension reducing polar co-solvent agent is alsoconsidered a functional surface tension modifying agent (that is, it isaptly referred to as a “solvo-surfactant” that is a low molecularweight, volatile solvent with an amphiphilic composition capable ofreducing fluid surface tension and capable of self-aggregating). On amolar and mass fraction basis, such solvo-solvents are less effectivesurface modifying agents than the traditional surfactants for reducingequilibrium surface tension. Solvo-surfactants employed for removal ofdried aqueous inkjet ink composition desirably comprise an asymmetricpolyhydric alcohol or mono-alkyl ether derived from a polyhydricalcohol. Specific examples of lower (C₁-C₄) mono-alkyl ethers andderivatives originating from polyhydric alcohols include but are notlimited to ethylene glycol monomethyl ether, ethylene glycol monobutylether, ethylene glycol monoethyl ether acetate, diethylene glycolmonomethyl ether, diethylene glycol monobutyl ether, triethylene glycolmonobutyl ether, polyethylene glycol monobutyl ether, propylene glycolmonomethyl ether, propylene glycol monopropyl ether and diethyleneglycol monobutyl ether acetate, among others all as supplied as theDOWANOL, CELLUSOLVE® and CARBITOL® series of compounds by Dow ChemicalCo. Such solvo-surfactants, alone or in combination, can be used atamounts of at least 0.1 weight % and up to and including 20 weight %, oreven in an amount of at least 3 weight % and up to and including 6weight %, all based on the total weight of the aqueous particle-freefluid.

Increased fluid pH can be beneficial to the removal of dried aqueousinkjet ink composition, and printhead cleaner aqueous particle-free pHis optionally raised with organic bases, such as aliphatic aminessubstituted with hydroxyl groups (for example, alkanolamines), includingmonoethanolamine, diethanolamine, 3-amino-1-propanol,N-methylethanolamine, N-benzyl-N-methylethanolamine,2-(2-aminoethoxy)ethanol, N,N-dimethyl-2-(2-aminoethoxy)ethanol,N-methyldiethanolamine, N,N-dimethylethanolamine, and triethanolamine.High pH aqueous particle-free fluids can have a pH of at least 10 and upto and including 11.

The wetting of contaminated printhead parts is critical to successfulcleaning. If sufficient solvo-surfactant is employed, no additionaldynamic or static surface tension modifier may be needed. Otherwise, asurfactant can be included. Representative compounds of these types aredescribed in Col. 12 (lines 27-62) of U.S. Pat. No. 8,764,161 (notedabove), the disclosure of which is incorporated herein by reference. Oneor more surfactants that may be anionic, cationic, amphoteric ornonionic in nature can be present in the aqueous particle-free fluid inan amount of at least 0.01 weight % and up to and including 10 weight %,based on the total weight of the aqueous particle-free fluid. While anyagent that serves to control the surface tension at large surface agescan be usefully employed, the surfactant desirably has aweight-normalized molecular weight below about 1,000 Daltons. While thecharged surfactants may have slower diffusion in aqueous fluids due tothe aggregated water of hydration which effectively increases theirbound mass, the useful non-ionic surfactants desirably have a molecularweight above 350 Daltons, above 400 Daltons, or even above 500 Daltons,to ensure slow diffusion in bulk ink to allow distinct control of staticor equilibrium surface tensions. Examples of suitable nonionicsurfactants include but are not limited to, linear or secondary alcoholethoxylates (such as the TERGITOL® 15-S and TERGITOL® TMN series ofcompounds available from Dow Chemical Company and the BRIJ® series ofcompounds from Croda International Plc.), ethoxylated alkyl phenols(such as the TRITONR series of compounds from Dow Chemical Company),fluoro surfactants (such as the ZONYL® compounds from DuPont; and theFLUORAD® compounds from 3M), fatty acid ethoxylates, fatty amideethoxylates, ethoxylated and propoxylated block copolymers (such as thePLURONIC and TETRONIC® series of compounds from BASF Corp., ethoxylatedand propoxylated silicone based surfactants (such as the SILWET® seriesof compounds from Momentive), alkyl polyglycosides (such as theGLUCOPONS compounds from BASF Corp.) and acetylenic diol polyethyleneoxide surfactants (such as the SURFYNOL® family of compounds from EvonikCorp.). The polymeric surfactants may be water soluble or waterdispersible depending in part on their tendency to aggregate. A usefulsurfactant blend suitable for dispersing pigments and re-dispersingdried aqueous inkjet ink compound is ZETASPERSE® 1600 (Evonik Corp.).

In addition, styrene-acrylic type polymers can be used in the printheadcleaner and storage fluid. The water-soluble or water-dispersiblepolymeric components can be the same or similar to the polymersdescribed above for use as polymeric dispersants for pigment colorants,or the anionic polymers incorporated into aqueous inkjet inkcompositions. Such materials are present in the aqueous inkjet inkcompositions to improve physical durability of an inkjet printed image,or to improve other characteristics of the compositions such ascolloidal stability to gear pump mediated recirculating filtration. Forexample, such water-soluble or water-dispersible polymeric componentscan be random or block copolymers having both hydrophilic andhydrophobic recurring units derived from the corresponding ethylenicallyunsaturated polymerizable monomers. They can be “acrylics” and“styrene-acrylics” that are derived primarily from styrene monomers, and(meth)acrylic acid, or (meth)acrylate ester monomers. Some usefulwater-soluble or water-dispersible polymeric components can be derivedfrom the various monomers and teaching provided in Col. 7 (line 24) toCol. 8 (line 55) of U.S. Pat. No. 8,764,161 (noted above). Other useful(3) water-soluble or water-dispersible polymeric compounds can bewater-soluble polymers having poly(ethylene-oxide) segments andwater-dispersible polyurethanes, for example, as described in Col. 10(lines 24-46) of U.S. Pat. No. 8,764,161 (noted above). Mixtures of twoor more of the same or different classes of these materials can be usedif desired.

One or more water-soluble or water-dispersible polymeric components canbe present in each aqueous particle-free fluid independently in anamount of up to and including 20 weight %, or at least 0.2 weight % andup to and including 10 weight %, or even at least 0.5 weight % and up toand including 8 weight %, or more likely in an amount of at least 2weight % and up to and including 5 weight %, all based on the totalweight of the aqueous particle-free fluid.

The aqueous particle-free fluids used for printhead cleaning and storageservice desirably contain a humectant, co-solvent, or both, tofacilitate inkjet printing start-up after an extended period of timewithout printing. Any water-soluble humectant or co-solvent known in theinkjet art and compatible with the other requirements of the inventioncan be employed. By water-soluble is meant that a mixture of theemployed humectant(s) or co-solvent(s) and water are adequatelyhomogeneous and not subject to spontaneous phase separation. While anindividual humectant or co-solvent can be employed, useful aqueousparticle-free fluid compositions can employ mixtures of two, three, ormore humectants and co-solvents, each of which imparts a usefulproperty. Representative examples of humectants and co-solvents used inaqueous-based ink compositions include (1) alcohols, such as methylalcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butylalcohol, sec-butyl alcohol, t-butyl alcohol, iso-butyl alcohol, furfurylalcohol, and tetrahydrofurfuryl alcohol; (2) polyhydric alcohols, suchas ethylene glycol, di(ethylene glycol), tri(ethylene glycol),tetra(ethylene glycol), propylene glycol, di(propylene glycol), thepoly(ethylene glycol)s with average molecular weights ranging from 200to about 5000 Daltons (particularly poly(ethylene glycol)-400 (averageM_(n) of about 400, herein referred to as PEG-400 for convenience)), thepolypropylene glycols with average molecular weights ranging from 200 toabout 5000 Daltons (particularly poly(propylene glycol)-425 (averageM_(n) of about 425)), 1,2-propanediol, 1,3-propanediol, 1,2-butanediol,1,3-butanediol, 1,4-butanediol, 1,2,4-butanetriol,3-methyl-1,3-butanediol, 2-methyl-1,3-propanediol, 1,5-pentanediol,1,6-hexanediol, 2-methyl-2,4-pentanediol, 1,7-heptanediol,2-ethyl-1,3-hexanediol, 2,2,4-trimethyl-1,3-pentanediol, 1,8-octanediol,glycerol, 1,2,6-hexanetriol, 2-ethyl-2-hydroxymethyl-propanediol,2-methyl-2-hydroxymethyl-propanediol, saccharides and sugar alcohols andthioglycol; (3) polyoxygenated polyols and their derivatives such asdiglycerol, polyglycerols, glycerol ethoxides, glycerol propoxides,glyceryths, alkylated and acetylated glyceryths, saccharide such assorbitol or fructose, pentaerythritol, pentaerythritol ethoxides, andpentaerythritol propoxides and their alkylated and acetylatedderivatives. Particularly desirable ingredients serving primarily as ahumectant to retard aqueous particle-free fluid drying and aid aqueousinkjet ink composition redispersability include glycerol, ethyleneglycol, diethylene glycol, triethylene glycol, related polyols, and thepolyhydric alcohol derivatives thereof, which are desirable. Triethyleneglycol is particularly useful. The total humectant and co-solvent levelof the fluid or ink is the sum of the individual contributions ofhumectant or miscible polar organic co-solvent, DST-modifying co-solvent(solvo-surfactant), and any other co-solvent ingredients, which mayinclude humectant or organic co-solvent added directly or incidentallyduring the totality of aqueous particle-free fluid or ink formulation(for example, co-solvent associated with a commercial biocidepreparation as a supplemental ingredient, or with a commercial pigmentdispersion preparation that may be present to prevent so-called“paint-flakes” of dried pigment cake forming around a bottle cap, asdescribed in U.S. Publication No. 2005/0075415 (Harz et al). The one ormore (c) humectants, co-solvents, or both humectants and co-solvents canbe present in the aqueous particle-free fluid in an amount of less than20 weight %, or of at least 0.5 weight %, or at least 1 weight % and upto and including 15 weight %, or at least 3 weight % and up to andincluding 10 weight %, all based on the total weight of the aqueousparticle-free fluid. More desirably, the total humectant and co-solventlevel is less than or equal to 10 weight %.

Each aqueous particle-free fluid can further contain one or morepromoters for the one or more compounds in the (b) compositionpotentially to enhance the effectiveness of the compounds represented byStructure (I). As described above, such promoters are generally alkanediols, each having at least 7 carbon atoms and up to and including 12carbon atoms, and particularly having at least 7 carbon atoms and up toand including 10 carbon atoms. Representative useful compounds that canbe used singly or in combination as promoters are described above.1,2-Octanediol is particularly useful as a promoter in this regard.

One or more promoters can be present in each aqueous particle-free fluidat a total amount of less than or equal to 1.5 weight % or less than orequal to 1.25 weight %, based on the total weight of the aqueous inkjetink composition. A minimum amount can be at least 0.3 weight %.

One or more (d) supplemental antimicrobial compounds can also be presentindependently in each aqueous particle-free fluid in a fluid set, andsuch materials are different from the (b) composition described above.Representative materials include but are not limited to, iodopropynylbutyl carbamate (CAS 55406-53-6), piroctone olamine (CAS 68890-66-4),2,4-dichlorobenzyl alcohol (CAS 1777-82-8), boric acid (CAS 10043-35-3)and monovalent and divalent metal ion salts derived from boric acid, andcombinations of any of these materials. A useful amount of the one ormore supplemental antimicrobial agents is at least 0.01 weight % and upto and including 3 weight %, based on the total weight of the aqueousparticle-free fluid.

Methods of Inkjet Printing

Details regarding the various methods and apparatus useful for inkjetprinting are provided in numerous publications, but none of that artdescribes such methods being carried out using the (b) compositionhaving compounds represented by Structure (I) defined above, or theadvantages achieved according to the present invention.

Methods according to the present invention are carried out firstly byprovide a suitable substrate (also known in the art as “receiver” or“receiver element”). Any individual substrate will have what would beunderstood as having at least one surface with a “printable” area ontowhich an aqueous inkjet ink composition can be ink jetted using suitableequipment and processes.

Suitable substrates are typically planar in nature with two opposingsurfaces or supporting sides, one or both of which can be inkjet-printedto provide the same or different images. Substrates can have a single“layer” or stratum or be composed of multiple layers or strata composedof the same or different materials. In most instances, a substrate has apredominant material, such as a cellulosic material that is coated orlayered with one or more other types of materials such as polymericcoatings.

For example, representative substrate can include but are not limitedto, photoglossy receivers or plain paper receivers such as bright whiteinkjet papers that are commercially available from various commercialsources (as described for example, in Col. 13, lines 28-34) of U.S. Pat.No. 8,187,371 (noted above). The photoglossy receivers (also known asswellable media or microporous media) can be manufactured with a coatedlayer on an underlying paper support and are also useful for providingphotographic quality inkjet-printed images. Some details of suchsubstrates are provided in Col. 13 (lines 37-51) of U.S. Pat. No.8,187,371 (noted above). Plain papers can be treated with multivalentsalts during or after manufacture as is well known in the art. Otheruseful substrates are described in U.S. Pat. No. 6,045,917 (Missell etal.), U.S. Pat. No. 5,605,750 (Romano et al.), U.S. Pat. No. 5,723,211(Romano et al.), and U.S. Pat. No. 5,789,070 (Shaw-Klein et al.), thedisclosures of all of which are incorporated herein by reference.

Useful paper substrates include plain bond papers, surface-treatedpapers, coated or calendared business gloss papers, resin-coated papers,laminated substrates comprising both paper layers and polymeric filmlayers such as polyester film layers, and heavy stock papers. It is alsopossible to use fabrics, cardboard or paperboard materials, organic orinorganic polymeric materials, microporous materials, non-wovensynthetics, and any other substrate material known in the art to forminkjet printable substrates. A substrate can be transparent,translucent, or opaque, and it can be provided for inkjet printing inthe form of a rigid or semi-rigid sheet, cut or continuous film or web,or wound roll.

Durability and other properties of inkjet-printed color images can beimproved by using substrates that have been pretreated with acomposition to enhance the quality of the resulting images. Thispretreatment is typically done prior to incorporation of the substrateinto the inkjet printing apparatus (such as a continuous inkjet printingapparatus), but in some instances, the substrate can be pretreatedwithin the apparatus before inkjet printing with one or more aqueousinkjet ink compositions. One or both opposing surfaces (planar sides) ofa substrate can be pretreated, or one supporting surface can bepretreated and the opposite supporting surface left untreated.

For example, a substrate can be pretreated with a pretreatmentcomposition comprising a water-soluble multivalent metal ion salt, suchas but not limited to, a salt comprising one or more multivalent cationsincluding calcium, magnesium, barium, zinc, and aluminum cations, withcalcium and magnesium cations being particularly useful. Examples ofuseful multivalent metal cation salts to provide such cations are knownin the art as useful salts can be determined by a skilled artisan.Details of such pretreatment procedures and compositions are providedfor example, in U.S. Pat. No. 9,067,448 (Dannhauser et al.), thedisclosure of which is incorporated herein by reference.

Each aqueous inkjet ink composition according to the present invention[as described above having the required viscosity and all (a)polymer-dispersed pigment colorant(s), (b) composition consisting ofStructure (I) compounds, and (c) compounds] can be inkjet-printed from asuitable printhead in a controlled manner onto at least one surface ofthe substrate to provide an inkjet-printed image on that surface of thesubstrate.

While the aqueous inkjet ink compositions according to this inventionmay be useful in one or more DOD printing systems, the advantages areparticularly evident when the present invention is carried out using CIJprinting processes and equipment. There are several CIJ printingprocesses known in the art, and the present invention is not limited toa CIJ process, but there may be certain CIJ processes that are moreuseful than others in carrying out the present invention. In general,such CIJ processes use one or more aqueous inkjet ink compositions thatare ejected through one or more printheads (containing nozzles) andunprinted aqueous inkjet ink composition is collected and recycledthrough the printing system multiple times until it is used up. Inaddition, the CIJ printing system can have incorporated replenishersystems. Details of such CIJ processes and equipment are provided forexample in U.S. Pat. No. 8,173,215 (noted above).

Thus, in most CIJ inkjet printing processes, each aqueous inkjet inkcomposition according to the present invention is ejected or printedfrom a main fluid supply dedicated to it only, as a continuous stream ofthe aqueous inkjet ink composition that is broken into both printingdrops and non-printing drops. The non-printing drops of each aqueousinkjet ink composition can be collected using suitable collecting meanssuch as a “catcher” and returned to its respective main fluid supply.This entire scenario can be carried out using a single (first) aqueousinkjet ink composition alone, or in combination with one or more“additional” aqueous inkjet ink compositions having the same ordifferent “colors” or hues as the first aqueous inkjet ink composition.The multiple aqueous inkjet ink compositions are then inkjet printed ina chosen sequence that can be controlled by particular software anddigital input, in a controlled manner, to provide a multicolor inkjetprinted-image on the surface of the substrate.

In addition, inkjet printing of an aqueous “colorless” or aqueousparticle-free composition or fluid (as described above) can be carriedout simultaneously or sequentially with inkjet printing of the “colored”aqueous inkjet ink composition(s). For example, according to U.S. PatentApplication Publication 2018/0051184 (Lussier et al.), a colorlesslacquer or protective coating can be applied over single- or multi-colorinkjet-printed images.

As is implied herein, each aqueous inkjet ink composition, aqueouscolorless composition, or aqueous particle-free composition of fluidused in such processes can be designed according to the presentinvention to comprise the described (a) one or more polymer-dispersedpigment colorants (only for the aqueous inkjet ink compositions),described (b) composition consisting of compounds defined by Structure(I), and described (c) compounds. However, all such aqueous compositionsused in the method according to the present invention can furtherinclude one or more (d) supplemental antimicrobial compounds that areall different from the (b) composition.

Useful CIJ printing processes and equipment can include replenishmentsystems that measure ink electrical resistivity and are described forexample in U.S. Pat. No. 5,526,026 (Bowers), the disclosure of which isincorporated herein by reference and in EP 0597628B1 (Loyd et al.).Useful CIJ printing processes and equipment that employ other means forink concentration sensing are disclosed in U.S. Pat. No. 7,221,440(McCann et al.), the disclosure of which is incorporated herein byreference, and in EP 0571784B1 (McCann et al.) and EP 1,013,450B1(Woolard et al.).

In one embodiment, basic replenishment is carried out as follows: afluid system contains an ink resistivity measurement cell through whichaqueous inkjet ink composition passes as it is being recirculatedthrough the ink handling portion of the system, including the printhead.A calculation means determines the resistance of the ink resistivitycell. A logic and control unit, responsive to the calculation means,controls the transfer of aqueous inkjet ink composition from asupplemental “ink” supply and the transfer of an aqueous particle-freefluid (“carrier fluid”) from a replenishment carrier fluid supply to thesystem main fluid supply, to maintain desired resistivity in the aqueousinkjet ink composition. The volume of the aqueous inkjet ink compositionis monitored by a float valve position, and when a predetermined volumehas been depleted, the predetermined volume is replaced by eitheraqueous inkjet ink composition from the supplemental “ink” supply or bycarrier fluid from the replenishment carrier fluid supply.

Thus, the first and any additional aqueous inkjet ink compositions canbe replenished, respectively, with first and any additional aqueousinkjet ink compositions, each of which consists essentially of the sameor different (a), (b), and (c) components described above, andespecially the same or different (b) composition that consists ofcompounds defined by Structure (I) noted above.

In other examples, the method according to the present invention canfurther comprise replenishing a main fluid supply with an aqueousparticle-free fluid that has a dynamic viscosity of less than or equalto 5 centipoise (5 mPa-sec) at 25° C., which aqueous particle-free fluidconsists essentially of:

the same or different (b) composition that is present in the firstaqueous inkjet ink composition, as described above.

Such aqueous particle-free fluid can further comprise a (d) supplementalantimicrobial compound, as described above, that is different from the(b) composition. For example, the (d) supplemental antimicrobialcompound can be iodopropynyl butyl carbamate, piroctone olamine,2,4-dichlorobenzyl alcohol, boric acid, or a combination of thesecompounds.

The aqueous particle-free fluid used for replenishment can also containone or more promoters for the one or more (b) compounds, each of whichpromoter is an alkane diol having a least 7 carbon atoms and up to andincluding 12 carbon atoms, in an amount of less than or equal to 1.5weight %, based on the total weight of the aqueous inkjet inkcomposition. For example, the promoter can be 1,2-octanediol.

In some embodiments, the method according to the present invention iscarried out using a plurality of printing drops formed from a continuousfluid stream, and non-printing drops of a different volume than theprinting drops are diverted by a drop deflection means into a “gutter”for collection and recirculation. Details about such CIJ printingsystems and equipment are provided for example in U.S. Pat. No.6,588,888 (Jeanmaire et al.), U.S. Pat. No. 6,554,410 (Jeanmaire etal.), U.S. Pat. No. 6,682,182 (Jeanmaire et al.), U.S. Pat. No.6,793,328 (Jeanmaire et al.), U.S. Pat. No. 6,866,370 (Jeanmaire etal.), U.S. Pat. No. 6,575,566 (Jeanmaire et al.), and U.S. Pat. No.6,517,197 (Hawkins et al.), and in U.S. Patent Application Publications2002/0202054 (Jeanmaire et al.), the disclosures of all of which areincorporated herein by reference.

In other embodiments, an aqueous inkjet ink composition can be printedusing an apparatus capable of controlling the direction of the formedprinting drops and non-printing drops by asymmetric application of heatto the fluid stream that initializes drop breakup and serves to steerthe resultant drop as described for example in U.S. Pat. No. 6,079,821(Chwalek et al.) and U.S. Pat. No. 6,505,921 (Chwalek), the disclosureof both of which are incorporated herein by reference. Useful agitation,heated supply, printhead, and fluid filtration means for CIJ printingare described for example in U.S. Pat. No. 6,817,705 (Crockett et al.),the disclosure of which is incorporated herein by reference.

A simple schematic of a CIJ printing system is provided in FIG. 1 ofU.S. Pat. No. 8,764,161 (noted above).

Moreover, in some embodiments, the method according to the presentinvention further comprises:

stopping the inkjet printing of the first aqueous inkjet inkcomposition;

delivering an aqueous particle-free fluid (as described above) from amaintenance fluid supply to the printhead; and

ejecting the aqueous particle-free fluid from the printhead to purge thefirst aqueous inkjet ink composition from the printhead,

wherein the aqueous particle-free fluid that has a dynamic viscosity ofless than or equal to 5 centipoise (5 mPa-sec) at 25° C. as measuredusing a rolling ball viscometer and consists essentially of:

the same or different (b) composition that is present in the firstaqueous inkjet ink composition, as described above.

Such aqueous particle-free fluid can further contain less than or equalto 15 weight % of one or more compounds selected from water-solublehumectants, co-solvents, and both water-soluble humectants andco-solvents, based on the total weight of the aqueous particle-freefluid.

Moreover, it can further contain one or more promoters for the (b)composition, each of which promoter is an alkane diol having a least 7carbon atoms and up to and including 12 carbon atoms, in an amount ofless than or equal to 1.5 weight %, based on the total weight of theaqueous particle-free fluid.

The aqueous particle-free fluid used in this series of steps can beconsidered a “maintenance fluid” that is used to clean the printheads atselected intervals or when a printing job is completed or interruptedfor some reason. The maintenance fluid can be stored in a printhead fora period of time, and delivery of first or additional aqueous inkjet inkcompositions from the main and any other respective fluid supplies tothe respective printheads can be subsequently restarted for a newprinting procedure.

Further details about use of an aqueous particle-free composition as amaintenance fluid in this manner are provided in U.S. Pat. No. 8,764,161(noted above).

According to some embodiments of this invention, a method of printing animage using a continuous inkjet printer system, can comprise:

providing a substrate (as described above);

providing a jetting module having a plurality of nozzles including anozzle in fluid communication with a main fluid supply containing afirst aqueous inkjet ink composition [such equipment would be readilyknown to one skilled in the art in view of teaching in U.S. Pat. No.9,010,909 (Nelson et al.) the disclosure of which is incorporated hereinby reference];

causing drops of the first aqueous inkjet ink composition to be formedwhile it is jetted through the nozzle in fluid communication with themain fluid supply by drop stimulation in response to time-varyingelectrical signals [equipment used to perform this function would bereadily apparent to one skilled in the art in view of teaching in U.S.Pat. No. 9,010,909 (Nelson et al.)];

providing a catcher including a drop contact face [known to one skilledin the art in view of teaching in U.S. Pat. No. 9,010,909 (notedabove)];

using a deflection mechanism to deflect at least some of the drops ofthe first aqueous inkjet ink composition onto the drop contact face ofthe catcher while allowing other drops of the first aqueous inkjet inkcomposition to pass by the catcher and to be deposited onto a surface ofthe substrate [known to one skilled in the art in view of teaching inU.S. Pat. No. 9,010,909 (noted above)]; and

causing the drops of the aqueous inkjet ink composition that contact thedrop contact face to flow along the drop contact face [known to knownskilled in the art in view of teaching in U.S. Pat. No. 9,010,909 (notedabove)],

wherein the first aqueous inkjet ink composition has a dynamic viscosityof less than or equal to 5 centipoise (5 mPa-sec) at 25° C., andconsists essentially of:

(a) one or more polymer-dispersed pigment colorants (as described above)in a total amount of at least 0.9 weight % and up to and including 6weight %, based on the total weight of the aqueous inkjet inkcomposition;

(b) a composition (as described above) consisting of one or morecompounds represented by the following Structure (I):

HO—CH₂—CH₂—R   (I)

wherein R is a substituted or unsubstituted phenyl group or asubstituted or unsubstituted phenoxy group, in a total amount of atleast 0.5 weight % and up to and including 2 weight %, based on thetotal weight of the aqueous inkjet ink composition;

(c) less than or equal to 15 weight % of one or more compounds (asdescribed above) selected from water-soluble humectants, co-solvents,and both water-soluble humectants and co-solvents, based on the totalweight of the aqueous inkjet composition,

wherein each of the one or more polymer-dispersed pigment colorants hasa 50^(th) percentile particle diameter of less than 70 nm and a 95^(th)percentile particle diameter of less than 150 nm, all particle diametersbeing measured using a dynamic light scattering particle size analyzer.

In some embodiments, the least some of the drops (deflected drops) ofthe first aqueous inkjet ink composition used in the noted method, aresmaller than the other drops (non-deflected and deposited drops) of thefirst aqueous inkjet ink composition.

In still other embodiments, the least some of the drops (deflecteddrops) of the first aqueous inkjet ink composition are larger than theother drops (non-deflected and deposited drops) of the first aqueousinkjet ink composition.

Moreover, a method according to the present invention for continuousinkjet (CIJ) printing can comprise:

supplying a main fluid supply of a continuous inkjet printer (as knownin the art) with a first aqueous inkjet ink composition (as describedabove) having a dynamic viscosity of less than or equal to 5 centipoise(5 mPa-sec) at 25° C., and consisting essentially of:

(a) one or more polymer-dispersed pigment colorants (as described above)in a total amount of at least 0.9 weight % and up to and including 6weight %, based on the total weight of the aqueous inkjet inkcomposition;

(b) a composition (as described above) consisting of one or morecompounds represented by the following Structure (I):

HO—CH₂—CH₂—R   (I)

wherein R is a substituted or unsubstituted phenyl group or asubstituted or unsubstituted phenoxy group, in a total amount of atleast 0.5 weight % and up to and including 2 weight %, based on thetotal weight of the aqueous inkjet ink composition;

(c) less than or equal to 15 weight % of one or more compounds (asdescribed above) selected from water-soluble humectants, co-solvents,and both water-soluble humectants and co-solvents, based on the totalweight of the aqueous inkjet composition,

wherein each of the one or more polymer-dispersed pigment colorants hasa 50^(th) percentile particle diameter of less than 70 nm and a 95^(th)percentile particle diameter of less than 150 nm, all particle diametersbeing measured using a dynamic light scattering particle size analyzer;

ejecting a continuous stream of drops of the first aqueous inkjet inkcomposition from a drop generator mechanism (as known in the art);

in response to electrical signals received from a control mechanism,selecting between printing drops for imaging a substrate and nonprintingdrops that are collected and returned to the main fluid supply, bothtypes of drops from the first aqueous inkjet ink composition; and

replenishing the main fluid supply as a function of resistivity of thefirst aqueous inkjet ink composition in the main fluid supply.Replenishment can be achieved using replenishing first aqueous inkjetink composition, or a replenishing aqueous particle-free fluid, asdescribed above.

Additional CIJ printing processes and details of useful CIJ apparatusare described for example in U.S. Pat. No. 8,585,189 (Marcus et al.),U.S. Pat. No. 8,651,632 (Marcus et al.), U.S. Pat. No. 8,696,094 (Marcuset al.), U.S. Pat. No. 8,888,256 (Marcus), and U.S. Pat. No. 9,969,178(Roberts et al.), all of which disclosures are incorporated herein byreference.

Printed Articles

A resulting inkjet printed article (or printed receiver element) canhave a monochrome or multi-color image on at least one supportingsurface of an article, including but not limited to, documents, papercurrency, postage stamps, packaging materials, fabrics, polymeric filmsor sheets, non-woven webs or sheets, labels for clothing, perfume, orwine bottles labels, lottery tickets, passports, drivers licenses, andother articles or papers that would be readily apparent to one skilledin the art using the teaching provided herein.

The present invention provides at least the following embodiments andcombinations thereof, but other combinations of features are consideredto be within the present invention as a skilled artisan would appreciatefrom the teaching of this disclosure:

1. An aqueous inkjet ink composition having a dynamic viscosity of lessthan or equal to 5 centipoise (5 mPa-sec) at 25° C., and consistingessentially of:

(a) one or more polymer-dispersed pigment colorants in a total amount ofat least 0.9 weight % and up to and including 6 weight %, based on thetotal weight of the aqueous inkjet ink composition;

(b) a composition consisting of one or more compounds represented by thefollowing Structure (I):

HO—CH₂—CH₂—R   (I)

wherein R is a substituted or unsubstituted phenyl group or asubstituted or unsubstituted phenoxy group, in a total amount of atleast 0.5 weight % and up to and including 2 weight %, based on thetotal weight of the aqueous inkjet ink composition;

(c) one or more compounds selected from water-soluble humectants,co-solvents, and both water-soluble humectants and co-solvents, in anamount of less than or equal to 20 weight %, based on the total weightof the aqueous inkjet composition,

wherein each of the one or more polymer-dispersed pigment colorants hasa 50^(th) percentile particle diameter of less than 70 nm and a 95^(th)percentile particle diameter of less than 150 nm, all particle diametersbeing measured using a dynamic light scattering particle size analyzer.

2. The aqueous inkjet ink composition of embodiment 1, furthercomprising a (d) supplemental antimicrobial agent that is different fromthe (b) composition.

3. The aqueous inkjet ink composition of embodiment 2, wherein the (d)supplemental antimicrobial agent is iodopropynyl butyl carbamate,piroctone olamine, 2,4-dichlorobenzyl alcohol, boric acid or a metal ionsalt derived from boric acid, or a combination these compounds.

4. The aqueous inkjet ink composition of any of embodiments 1 to 3,wherein the (a) one or more polymer-dispersed pigment colorants arepresent in a total amount of least 1.5 weight % and up to and including5 weight %, based on the total weight of the aqueous inkjet inkcomposition.

5. The aqueous inkjet ink composition of any of embodiments 1 to 4,wherein the one or more (c) compounds are present in an amount of least0.5 weight % and up to and including 15 weight %, based on the totalweight of the aqueous inkjet ink composition.

6. The aqueous inkjet ink composition of any of embodiments 1 to 5,further containing an anionic polyurethane, an anionic non-aromaticacrylic polymer, an anionic styrene-acrylic polymer, or a combination oftwo or more of such materials, each of these materials having an acidnumber of at least 50.

7. The aqueous inkjet ink composition of any of embodiments 1 to 6,wherein each of the one or more polymer-dispersed pigment colorants hasa 50^(th) percentile particle diameter of less than 60 nm and a 95^(th)percentile particle diameter of less than 110 nm, all particle diametersbeing measured using a dynamic laser light scattering particle sizeanalyzer.

8. The aqueous inkjet ink composition of any of embodiments 1 to 7having a pH of at least 7.5 and up to and including 11.

9. The aqueous inkjet ink composition of any of embodiments 1 to 8,having a dynamic viscosity of at least 1 centipoise (1 mPa-sec) and upto and including 3 centipoise (3 mPa-sec) at 25° C.

10. The aqueous inkjet ink composition of any of embodiments 1 to 9,further containing one or more promoters for the one or more Structure(I) compounds in the (b) composition, each of which promoter is analkane diol having a least 7 carbon atoms and up to and including 12carbon atoms, in an amount of less than or equal to 1.5 weight %, basedon the total weight of the aqueous inkjet ink composition.

11. The aqueous inkjet ink composition of any of embodiments 1 to 10,further containing one or more promoters for the one or more Structure(I) compounds of the (b) composition, each of which promoters is analkane diol having a least 7 carbon atoms and up to and including 10carbon atoms, in an amount of less than or equal to 1.25 weight %, basedon the total weight of the aqueous inkjet ink composition.

12. The aqueous inkjet ink composition of embodiment 10, wherein thepromoter is 1,2-octanediol.

13. The aqueous inkjet ink composition of any of embodiments 1 to 12,wherein R is either an unsubstituted phenyl group or an unsubstitutedphenoxy group.

14 An ink set comprising two or more aqueous inkjet ink compositions,each of which independently has a dynamic viscosity of less than orequal to 5 centipoise (5 mPa-sec) at 25° C., and each of which aqueousinkjet ink compositions independently consists essentially of:

(a) one or more polymer-dispersed pigment colorants in a total amount ofat least 0.9 weight % and up to and including 6 weight %, based on thetotal weight of the aqueous inkjet ink composition;

(b) a composition consisting of one or more compounds represented by thefollowing Structure (I):

HO—CH₂—CH₂—R   (I)

wherein R is a substituted or unsubstituted phenyl group or asubstituted or unsubstituted phenoxy group, in a total amount of atleast 0.5 weight % and up to and including 2 weight %, based on thetotal weight of the aqueous inkjet ink composition;

(c) one or more compounds selected from water-soluble humectants,co-solvents, and a combination of water-soluble humectants andco-solvents, in an amount of less than or equal to 20 weight %, based onthe total weight of the aqueous inkjet composition,

wherein each of the one or more polymer-dispersed pigment colorants hasa 50^(th) percentile particle diameter of less than or equal to 70 nmand a 95^(th) percentile particle diameter of less than or equal to 150nm, all particle diameters being measured using a dynamic lightscattering particle size analyzer.

15. The ink set of embodiment 14, comprising two or more of thefollowing:

(i) an aqueous inkjet ink composition comprising a polymer-dispersedcyan pigment colorant,

(ii) an aqueous inkjet ink composition comprising a polymer-dispersedmagenta pigment colorant,

(iii) an aqueous inkjet ink composition comprising a polymer-dispersedyellow pigment colorant, and

(iv) an aqueous inkjet ink composition comprising a polymer-dispersedblack pigment colorant.

16. The ink set of embodiment 15, comprising all four (i) through (iv)aqueous inkjet ink compositions.

17. The ink set of any of embodiments 14 to 16, further comprising aparticle-free colorless inkjet composition.

18. The ink set of embodiment 17, wherein the particle-free colorlessinkjet composition comprises the same or different (b) composition as ispresent in each of the two or more aqueous inkjet ink compositions.

19. The ink set of any of embodiments 14 to 18, wherein any of the twoor more aqueous inkjet ink compositions further contains a (d)supplemental antimicrobial agent that is different from the (b)composition.

20. The ink set of embodiment 19, wherein the (d) supplementalantimicrobial agent is iodopropynyl butyl carbamate, piroctone olamine,2,4-dichlorobenzyl alcohol, boric acid or metal ion salt derived fromboric acid, or a combination of these compounds.

21. The ink set of any of embodiments 14 to 20, wherein the (a) one ormore polymer-dispersed pigment colorants are present independently ineach of the two or more aqueous inkjet ink compositions, in a totalamount of least 1.5 weight % and up to and including 5 weight %, basedon the total weight of the aqueous inkjet ink composition.

22. The ink set of any of embodiments 14 to 21, wherein the one or more(c) compounds are present independently in each of the aqueous inkjetink compositions, in an amount of least 0.5 weight % and up to andincluding 15 weight %, based on the total weight of the aqueous inkjetink composition.

23. The ink set of any of embodiments 14 to 22, wherein any of the twoor more aqueous inkjet ink compositions, further contains an anionicpolyurethane, an anionic non-aromatic acrylic polymer, an anionicstyrene-acrylic polymer, or a combination of two or more of suchmaterials, each of these materials having an acid number of at least 50.

24. The ink set of any of embodiments 14 to 23, wherein each of the oneor more polymer-dispersed pigment colorants has a 50^(th) percentileparticle diameter of less than 60 nm and a 95^(th) percentile particlediameter of less than 110 nm, all particle diameters being measuredusing a dynamic laser light scattering particle size analyzer.

25. The ink set of any of embodiments 14 to 24, wherein each of the twoor more aqueous inkjet ink compositions independently has a pH of atleast 7.5 and up to and including 11.

26. The ink set of any of embodiments 14 to 25, wherein each of the twoor more aqueous inkjet ink compositions independently has a dynamicviscosity of at least 1 centipoise (1 mPa-sec) and up to and including 3centipoise (3 mPa-sec) at 25° C.

27. The ink set of any of embodiments 14 to 26, wherein any of the twoor more aqueous inkjet ink compositions further contains one or morepromoters for the one or more Structure (I) compounds of the (b)composition, each of which promoters is an alkane diol having a least 7carbon atoms and up to and including 12 carbon atoms, in an amount ofless than or equal to 1.5 weight %, based on the total weight of theaqueous inkjet ink composition.

28. The ink set of embodiment 27 wherein the promoter is 1,2-octanediol.

29. The ink set of any of embodiments 1 to 28, wherein R is either anunsubstituted phenyl group or an unsubstituted phenoxy group.

The following working examples are provided to illustrate the practiceof one or more aspects and embodiments of the present invention.

In the following preparations and examples, the pigment dispersionreported pigment content is based on the weight percent of theas-received colorant in the final dispersion.

Preparation of Aqueous Inkjet Ink and Service Fluid CompositionsPolymeric Dispersant and Additive Preparation:

Polymeric Dispersant P-1

In a representative procedure, a 5-liter, three-necked, round bottomflask equipped with a mechanical stirrer, a reflux condenser, and a gasinlet was charged with 225 g of 1-methoxy-2-propanol and was spargedwith nitrogen. Akzo-Nobel Chemicals, Inc., initiator PERKADOX® AMBN-GR(1.9 g) was added with stirring. A reactant reservoir was charged with225 g of 1-methoxy-2-propanol, 23.4 g of 1-dodecanethiol, 203.5 g ofbenzyl methacrylate, 165.0 g of stearyl methacrylate, and 181.5 g ofmethacrylic acid, and the solution was degassed by nitrogen sparging.PERKADOX® AMBN-GR (7.7 g) was added and mixed in. The reactortemperature was raised to 77° C. and the reactants were pumped from thereservoir at a about 2.3 ml/min over a 360-minute period. The reactionmixture was then stirred for at least 12 hours at about 77° C. Theresulting polymer was neutralized to completion withN,N-dimethylethanolamine and stirred for 45 minutes. The reactionmixture was diluted with 2,580 g of water and filtered through a PallCorp. UILTIPLEAT® polypropylene cartridge filter. The final polymersolution of Polymeric Dispersant P-1 had a concentration of about 20weight % solids and its pH was 8.6. The polymer weight-average molecularweight was 9,070 Daltons.

Polymeric Dispersant P-2

Polymeric dispersant P-2 was prepared in a similar fashion to P-1,except that 90% of the acid was reacted with potassium hydroxide duringthe neutralization step instead of with one equivalent ofN,N-dimethylethanolamine.

The final polymer solution of Polymeric Dispersant P-2 had aconcentration of about 17 weight % solids.

Polymeric Additive P-3

A benzyl methacrylate-methacrylic acid copolymer having monomer weightratio 77:23 and acid number of about 137 was 90%-neutralized withpotassium hydroxide to provide an aqueous solution. The final polymersolution of Polymeric Additive P-3 had a concentration of about 25weight % solids.

Polymeric Additive P-4

BASF Dispersions & Pigments North America JONCRYL® HPD 696, which is astyrene acrylic copolymer having a weight-average molecular weight M_(w)of 16,000 Daltons, was 90%-neutralized with potassium hydroxide toprovide an aqueous solution. The final polymer solution of PolymericAdditive P-4 had a concentration of about 20 weight % solids.

Polymeric Additive P-5

In a 50-liter, round bottom flask equipped with thermometer, stirrer,water condenser, nitrogen inlet, and a vacuum outlet were placed 1,454.4g of TERATHANE® 2000 polyether glycol, 670.5 g of 2,2-bis(hydroxymethyl)propionic acid, 313.2 g of 1,4-butanediol, and 3,771 g of ethyl acetate.The temperature was adjusted to 65° C., and when a homogeneous solutionwas obtained, 1,840.9 g of isophorone diisocyanate was added, followedby 184 g of ethyl acetate. The temperature was raised to 78° C. andmaintained for 22 hours to complete the reaction. The reaction mixturewas then diluted with 86 g of 2-propanol before being neutralized with467.9 g of N,N-dimethylethanolamine. Under high shear, 18 kg ofdistilled water were added and the organic solvents were subsequentlyremoved by distillation under vacuum. The resultant aqueous dispersionwas filtered and was determined to have a non-volatile solidsconcentration of about 25 weight % and a pH value of about 8.0. Theweight-average molecular weight (M_(w)) of the polyurethane dispersionwas found by size exclusion chromatography to be about 19,800.

Pigment Dispersion Preparations: Pigment Dispersion KD-1

To a 2.5-gallon (9.46 liter), 9-inch (22.9 cm) diameter and 12-inch(30.5 cm) deep, double-walled stainless-steel mixing vessel containingfour baffles were added water (1,000 g) and a solution of PolymericDispersant P-1 (1,000 g of a 19.9 weight % solution). A nominal 4-inch(10.2 cm), ring-style disperser impeller (Hockmeyer Equipment Corp.D-Blade) driven by a Charles Ross & Son Co. Model HSM-100LH-2 High ShearMixer was centered 2 inches (5.1 cm) above the bottom of the mixingvessel and stirring was initiated. Cabot Corp. BLACK PEARLS® 900 carbonblack pigment (500 g) was slowly integrated into the fluid. Millingmedia comprising beads of polystyrene resin (copolymer derived fromstyrene and a divinyl benzene/ethylvinyl benzene mixture) with anaverage particle diameter of 50 μm (3,000 g) was added slowly whileincreasing impeller speed. The mixture was milled with an impeller bladetip speed of about 19 m/sec for about 20 hours at an internaltemperature of 25-35° C. Samples were periodically removed, diluted, andfiltered for particle size determination by a Microtrac, Inc., NANOTRAC®NPA 150 dynamic light scattering particle size analyzer. When millingwas complete, the dispersion/media milling mixture was further dilutedwith a solution of water (1,667 g) to a final pigment concentration ofabout 12 weight %, a polymeric dispersant concentration of about 4.8weight % including the counterion, and a theoretical dispersion batchsize of about 4,167 g. The impeller was removed, and the milling mediawas separated from the dispersion by filtration. A final filtrationthrough a 0.3-μm removal efficiency Pall Corp. PROFILE II® depth filtergave roughly 4 kg of dispersion, approximately 80% yield. Thevolume-weighted 50^(th) percentile particle size distribution diameterwas about 55 nm, and the 95^(th) percentile particle size distributiondiameter was about 99 nm as characterized by the NANOTRAC® NPA 150dynamic light scattering particle sizing instrument.

Pigment Dispersion MD-1

Magenta pigment dispersion MD-1 was prepared in a similar manner topigment dispersion KD-1, except that BASF Dispersions & Pigments NorthAmerica CINQUASIA® Magenta D 4500 J was used in place of carbon blackpigment. The resulting dispersion had approximately 12 weight % pigmentand 6.1 weight % polymeric dispersant, including the counterion. Thevolume-weighted median particle size was about 16 nm and the 95^(th)percentile particle size distribution diameter was about 59 nm ascharacterized by the NANOTRAC® NPA 150 dynamic light scattering particlesizing instrument.

Pigment Dispersion CD-1

Cyan pigment dispersion CD-1 was prepared in a similar manner to pigmentdispersion KD-1, except that Pigment Blue 15:4 and Pigment Green 7 wereused in a ratio of 3.75:1 in place of carbon black pigment and polymericdispersant P-2 was used in place of P-1 in the presence of LubrizolCorp. SOLSPERSE® 12000 and Polymeric Additive P-3. The resultingdispersion had approximately 12 weight % pigment and 8.5 weight %polymer dispersant, including the counterion. The volume-weighted50^(th) percentile particle size distribution diameter is about 28 nm,and the 95^(th) percentile particle size distribution diameter is about86 nm as characterized by the NANOTRAC® NPA 150 dynamic light scatteringparticle sizing instrument.

Pigment Dispersion YD-1

To a 10-gallon (37.85 liter), 13-inch (33 cm) diameter and 17-inch (43.2cm) deep, double-walled stainless-steel mixing vessel containing fourbaffles were added 2,560 g water and 2,400 g of a 15% solution ofPolymeric Dispersant P-2. A nominal 6-inch (15.2 cm) ring-styledisperser impeller (Hockmeyer Equipment Corp. D-Blade) driven by aHockmeyer Model HBI-7.5-11-99 High Shear Mixer was centered 3 inches(7.6 cm) above the bottom of the mixing vessel and stirring wasinitiated. Sun Chemical Co. Pigment Yellow 74 (1,200 g) was slowly addedto the fluid. Milling media comprising polymeric beads derived fromstyrene and a divinyl benzene/ethylvinyl benzene mixture with an averageparticle diameter of 50 μm (7,200 g) were added slowly while increasingimpeller speed. The mixture was milled with an impeller blade tip speedof about 20 meters/second for about 20 hours at an internal temperatureof 25-30° C. The dispersion/media mixture was further diluted with water(6,000 g) to a final pigment concentration of about 12 weight % and aPolymeric Additive P-2 concentration of about 4.1 weight %. The impellerwas removed, and the dispersion was separated from the milling media byfiltration. A final filtration through a 0.3 μm particle removal ratingPall Corp. PROFILE II® depth filter yielded roughly 10.6 kg ofdispersion. The volume-weighted 50^(th) percentile particle sizedistribution diameter of the dispersion was about 11 nm, and the 95^(th)percentile particle size distribution diameter was about 16 nm asdetermined by a NANOTRAC® NPA 150 dynamic light scattering particlesizing instrument.

Preparation of Continuous Inkjet Ink and Service Fluid Compositions:Aqueous Black Inkjet Ink Composition

Black pigmented CIJ aqueous inkjet ink composition K-A (E) was preparedusing pigment dispersion KD-1 by combining the components at therelative proportions reported in the following TABLE I. In arepresentative procedure, 15.0 kg of aqueous inkjet ink composition wasmixed by adding the components individually to a 30-liter cross-linked,high density polyethylene flat bottom tank using a 2-inch (5.1 cm)impeller rotating at about 1,000 rpm to provide good mixing. Theingredients (if so indicated) were added in the following functionalcomponent order: water, acid or acid solution, amine-acid salt solution,humectant and organic co-solvent, amine base, metal corrosion inhibitor,preservative or biocide, solvo-surfactant, soluble azo dye, pigmentdispersion, surfactant, and antifoamant. The aqueous inkjet inkcomposition was mixed for about 2 minutes between ingredient additions,and then it was stirred for 1 hour after the final addition of thesurfactant or antifoamant. The aqueous inkjet ink composition wasfiltered through Pall Corp. 0.2 μm effective pore size ULTIPOR® N66cartridge filter media at a rate of about 0.5 liter/min/inch (0.2liter/min/cm) of media. The pigment particles in the resulting aqueousinkjet ink composition had a volume-weighted 50^(th) percentile particlesize of 53 nm and 95^(th) percentile particle size of 79 nm, a pH ofabout 8.6, electrical conductivity of 1.14 mS/cm, dynamic viscosity of1.60 mPa-sec at 25° C., density of 1.035 g/cm³ at 25° C., and a staticsurface tension of 37.2 mN/m at 25° C.

TABLE I Functional Ink K-A (E) Component Component (weight %) VehicleWater 48.8 Pigment Dispersion KD-1 33.8 Binder Polymer P-5 7.2Dispersion Humectant Glycerol 8.5 Metal Corrosion Inhibitor COBRATEC®0.1 TT-50S (PMC Specialties Group, Inc.) Solvo- 2-Phenylethanol 1.5surfactant (Acros Organics) Surfactant SURFYNOL® 440 0.2 (Evonik Corp.)

Aqueous Cyan Inkjet Ink Compositions

Aqueous cyan CIJ inkjet ink compositions C-A through C-C were preparedfrom the pigment dispersion CD-1 by combining the components at therelative proportions shown below in TABLE II in a manner analogous tothat described for the aqueous inkjet ink composition K-A. These inkjetink compositions exhibited physical properties that are reported belowin TABLE III.

TABLE II C-B (E) C-C (E) Functional C-A (C) (weight (weight ComponentIngredient (weight %) %) %) Vehicle Water 74.1 72.6 72.6 Pigment CD-116.7 16.7 16.7 Dispersion Binder Polymer P-5 4.0 4.0 4.0 DispersionStabilizer LUVITEC ® 0.5 0.5 0.5 Polymer K 17 (BASF) Humectant Glycerol4.0 4.0 4.0 Metal Corrosion COBRATEC ® 0.1 0.1 0.1 Inhibitor TT-50S (PMCSpecialties Group, Inc.) Solvo- 2-Phenoxyethanol 0.0 1.5 0.0 surfactant(Sigma-Aldrich) Solvo- 2-Phenylethanol 0.0 0.0 1.5 surfactant (AcrosOrganics) Surfactant SURFYNOL ® 440 0.1 0.1 0.1 (Evonik Corp.)Antifoamant SURFYNOL ® DF- 0.1 0.1 0.1 110D (Evonik Corp.)

TABLE III Properties C-A (C) C-B (E) C-C (E) Particle Size 28 29 3050^(th) percentile (nm) Particle Size 86 84 81 95^(th) percentile (nm)pH 8.5 8.4 8.4 Conductivity 1.99 2.05 2.12 (mS/cm) Density, 25° C. 1.0231.024 1.022 (g/cm³) Dynamic Viscosity, 1.34 1.40 1.40 at 25° C. inmPa-sec Static Surface 37.8 36.7 36.5 Tension, at 25° C. in mN/m

Aqueous Magenta Inkjet Ink Compositions

Aqueous magenta CIJ inkjet ink compositions M-A through M-C wereprepared from the pigment dispersion MD-1 by combining the components atthe relative proportions reported below in TABLE IV in a manneranalogous to that described for the aqueous black inkjet ink K-A. Theseaqueous magenta inkjet ink compositions exhibited physical propertiesthat are reported below in TABLE V.

TABLE IV M-A (C) M-B (E) M-C (E) Functional (weight (weight (weightComponent Component %) %) %) Vehicle Water 55.4 53.9 53.9 Pigment MD-131.7 31.7 31.7 Dispersion Binder Polymer P-5 6.0 6.0 6.0 DispersionHumectant Glycerol 6.5 6.5 6.5 Metal Corrosion COBRATEC ® 0.1 0.1 0.1Inhibitor TT-50S (PMC Specialties Group, Inc.) Solvo- 2-Phenoxyethanol0.0 1.5 0.0 surfactant (Sigma-Aldrich) Solvo- 2-Phenylethanol 0.0 0.01.5 surfactant (Acros Organics) Surfactant SURFYNOL ® 0.22 0.22 0.22 440(Evonik Corp.) Antifoamant SURFYNOL ® 0.1 0.1 0.1 DF-110D (Evonik Corp.)

TABLE V Properties M-A (C) M-B (E) M-C (E) Particle Size 15 14 1550^(th) percentile (nm) Particle Size 60 59 57 95^(th) percentile (nm)pH 8.7 8.6 8.6 Conductivity 1.51 1.50 1.52 (mS/cm) Density, 25° C. 1.0331.035 1.033 (g/cm³) Dynamic Viscosity, at 1.74 1.87 1.83 25° C. inmPa-sec Static Surface 38.7 37.1 36.8 Tension, at 25° C. in mN/m

Aqueous Yellow Inkjet Ink Composition

Aqueous yellow CIJ inkjet ink composition Y-A (E) was prepared from thepigment dispersion YD-1 by combining the components at the relativeproportions reported below in TABLE VI in a manner analogous to thatdescribed for the aqueous inkjet ink composition K-A.

TABLE VI Functional Y-A (E) Component Component (weight %) Vehicle Water60.9 Pigment Dispersion YD-1 25.0 Binder Polymer P-4 4.0 Solution BinderPolymer P-5 3.3 Dispersion Humectant Triethylene glycol 5.0 MetalCorrosion COBRATEC ® 0.1 Inhibitor TT-50S (PMC Specialties Group, Inc.)Solvo- 2-Phenylethanol 1.5 surfactant (Acros Organics) SurfactantSURFYNOL ® 440 0.1 (Evonik Corp.) Antifoamant SURFYNOL ® DF- 0.1 110D(Evonik Corp.)

The pigment particles in this aqueous inkjet ink composition had avolume-weighted 50^(th) percentile particle size of 12 nm and a 95^(th)percentile particle size of 31 nm as characterized by the NANOTRAC® NPA150 dynamic light scattering particle sizing instrument. It also had apH of about 8.4, electrical conductivity of 2.26 mS/cm, dynamicviscosity of 1.62 mPa-sec at 25° C., density of 1.020 g/cm³ at 25° C.,and a static surface tension of 36.3 mN/m at 25° C.

Continuous Inkjet Printing (CIJ) Replenisher Fluid

CIJ Replenisher Fluids R-A (E) and R-B (E) were prepared by combiningthe components shown below in TABLE VII at the relative proportions in amanner analogous to that described for aqueous black inkjet inkcomposition K-A. These aqueous particle-free fluids exhibited physicalproperties that are shown below in TABLE VIII.

TABLE VII Fluid R-A Fluid R-B Functional (E) (E) Component Component(weight %) (weight %) Vehicle Water 99.0 99.0 Solvo- 2-Phenoxyethanol1.0 0.0 surfactant (Dow Chemical Co.) Solvo- 2-Phenylethanol 0.0 1.0surfactant (Acros Organics)

TABLE VIII Properties Fluid R-A (E) Fluid R-B (E) pH 6.5 6.2Conductivity 0.001 0.001 (mS/cm) Density, at 25° C. in g/cm³ 0.999 0.998Dynamic Viscosity, at 1.018 0.923 25° C. in mPa-sec Static SurfaceTension, at 46.9 46.1 25° C. in mN/m

Continuous Inkjet Printing (CIJ) Printhead Cleaner and Storage Fluid

CIJ Printhead Cleaner and Storage Fluids S-A (C) and S-B (E) wereprepared by combining the components below in TABLE IX at the relativeproportions in a manner analogous to that described for the aqueousblack inkjet ink composition K-A. These aqueous particle-free fluidsexhibited physical properties that are shown below in TABLE X.

TABLE IX Fluid S-A Fluid S-B Functional (C) (E) Component Component(weight %) (weight %) Vehicle Water 83.7 81.3 Base N,N-Dimethyl- 0.1 0.5aminoethanol Acid Acetic acid, 25% 0.1 1.2 Humectant Triethylene glycol10.0 10.0 Metal Corrosion COBRATEC ® 0.1 0.1 Inhibitor TT-50S (PMCSpecialties Group, Inc.) Solvo- Diethylene glycol 5.0 5.0 surfactantmonobutyl ether Solvo- 2-Phenoxyethanol 0.0 1.0 surfactant (Dow ChemicalCo.) Surfactant ZETASPERSE ® 1.0 1.0 1600 (Evonik Corp.)

TABLE X Properties Fluid S-A (C) Fluid S-B (E) pH 9.2 8.6 Conductivity0.44 2.12 (mS/cm) Density, at 25° C. in 1.015 1.017 g/cm³ DynamicViscosity at 1.64 1.65 25° C. in mPa-sec Static Surface Tension, 28.329.3 at 25° C. in mN/m

Microbiological Growth Susceptibility Testing:

The aqueous inkjet ink compositions described above were subjected to aTen Challenge preservative efficacy test employing cultured strains ofparticular microorganisms. The test organisms were individually culturedto known concentrations of colony forming units (CFU) and they were thenmixed together and inoculated into 50 grams of the aqueous inkjet inkcomposition test sample. At specified time intervals, the inoculatedsample was tested. The surviving population of inoculum was evaluated bystreaking a Trypticase Soy Agar plate with 10 μl of well-mixed sampleand incubating. The presence of microorganisms was documented using thegrowth ratings shown in the following TABLE XI. Each sample wasre-inoculated and evaluated up to ten times over the course of thestudy, while any changes in the physical appearance of the sample wereobserved.

TABLE XI Microorganism Growth Rating Colonies 1 0 2 1 to 4 3  5 to 10 411 to 25 5 26 to 50 6  51 to 100 7 101 to 200 8 201 to 300 9 TNTC* 10Confluent growth *TNTC means “too numerous to count”

The following TABLE XII reports the 10 Challenge growth rating testresults for the previously described aqueous inkjet ink compositions(“ink”), wherein the initial baseline growth rating for microorganismsin the as-received composition was determined to be “1.” The columnidentified with “R—OH” denotes the absence or presence ofsolvo-surfactant 2-phenoxyethanol (PhE) or 2-phenylethanol (PEA) in thesample.

TABLE XII Entry Ink R—OH 1 2 3 4 5 6 7 8 9 10 1 (C) C-A — 9 9 6 9 6 9 99 9 6 2 (E) C-B PhE 1 1 1 1 1 2 1 2 1 1 3 (E) C-C PEA 1 1 1 1 1 1 1 1 11 4 (C) M-A — 1 4 2 2 5 4 5 4 2 2 5 (E) M-B PhE 1 1 1 1 1 1 1 1 1 1 6(E) M-C PEA 1 1 1 1 1 1 1 1 1 1 7 (E) Y-A PEA 1 1 1 1 1 1 1 1 1 1 8 (E)K-A PEA 1 1 1 1 1 1 1 1 1 1

The results shown in TABLE XII indicate that considerable microorganismgrowth (high colony counts) was observed in the comparative composition(“ink”) C-A (C) and M-A (C) after the first few inoculations. The datain TABLE XII also reveal that the presence of 2-phenoxyethanol (PhE) ininventive compositions (“Inks”) C-B (E) and M-B (E) or 2-phenylethanol(PEA) in inventive compositions (“Inks”) C-C (E), M-C (E), Y-A (E), andK-A (E) resulted in minimal or undetectable microbial growth through allten challenges.

In an identical manner to the aqueous inkjet ink compositions, theaqueous particle-free fluids were subjected to a Ten Challengepreservative efficacy test employing the same cultured strains ofparticular microorganisms. The following TABLE XIII shows the 10Challenge growth rating test results for those fluids, wherein theinitial baseline growth rating for microorganisms in the as-receivedfluids was determined to be “1”. The column identified with “R—OH”denotes the absence or presence of solvo-surfactant 2-phenoxyethanol(PhE) or 2-phenylethanol (PEA) in the fluid.

TABLE XIII Entry Fluid R—OH 1 2 3 4 5 6 7 8 9 10 1 (E) R-A PhE 1 2 4 7 52 1 2 2 4 2 (E) R-B PEA 2 1 1 1 1 6 6 6 4 6 3 (C) S-A — 1 1 1 1 1 1 3 11 1 4 (E) S-B PhE 1 1 1 1 1 1 1 1 1 1

The results reported in TABLE XIII show that significant microorganismgrowth (increased colony counts) was observed in the inventiveReplenisher Fluids R-A (E) and R-B (E) after the first few inoculations,but the result is expected to be better than a replenisher fluidcomprised purely of water without any solvo-surfactant. The results inTABLE XIII also show that virtually no microorganism growth was observedin the comparative Printhead Cleaning and Storage Fluid S-A (C), whichcontained solvo-surfactant diethylene glycol monobutyl ether as a driedink cleaning agent; only challenge No. 7 produced a significant growthrating of 3. However, the presence of 2-phenoxyethanol (PhE) ininventive Printhead Cleaning and Storage Fluid S-B (E) producedundetectable microbial growth through all ten challenges.

It will be appreciated that embodiments of aqueous inkjet inkcompositions and aqueous particle-free fluids according to the presentinvention can be suitably resistant to growth of contaminatingmicroorganisms without containing any substantial amounts of, that is,being substantially free of, commonly used preservatives such asisothiazolinone compounds and formaldehyde releasing compounds (forexample, 2-bromo-2-nitropropane-1, 3-diol and hexamethylenetetraminechloroallyl chloride) and biocides currently listed in the List ofApproved Active Substances (Article 95 List) published by the EuropeanChemical Agency (ECHA) (an agency of the European Union).

Continuous Inkjet Printing of Aqueous Inkjet Ink Compositions:

In a representative procedure, the ink reservoir of a continuous inkjetprinting test stand fixture was charged with inventive aqueous cyaninkjet ink composition C-C (E). Repetitive cycles of draining, flushing,and filling the ink reservoir and fluid lines with C-C (E) were carriedout to ensure that the new composition was not contaminated by the priorink in the apparatus. The fixture consisted of the following elements:(1) a fluid system capable of (a) pressurizing the composition (“ink”)in excess of 60 psid (0.41 MPa) thereby producing ink volumetric flowrates of up to about 2 liters/min; (b) delivering pressurized ink to acontinuous inkjet printhead drop generator; (c) returning unprinted inkunder vacuum to the fluid system ink reservoir; (d) detecting the inkreservoir ink concentration by electrical resistivity measurement andreplenishing the ink with inventive Replenisher Fluid R-B (E) ifconcentrated by water evaporation, and adding more aqueous inkjet inkcomposition C-C (E) to the ink reservoir instead if it was depleted byuse in printing but was at the correct concentration; (e) providing theprinthead with inventive Printhead Cleaning and Storage Fluid S-B (E) toflush the nozzles and duct systems in order to restore accurate printingafter fouling by dried ink build-up, and to shut down the system forsafe storage over significant time durations; (2) a vacuum drum capableof supporting a sheet of porous media (for example, uncoated free sheetpaper) or non-porous media (for example, coated or uncoated polymerfilm) and spinning it continuously at precise speeds synchronized with acontrol unit to simulate web transport of the printing substrate in rollform; (3) a continuous inkjet printhead PIC box assembly including (a) aKODAK PROSPER Press Jetting Module with a MEMS silicon-based dropgenerator to form drops of ink and a Coanda gutter to catch non-printingdrops when the printer is not printing an image file or when it is notprinting a given pixel even if it is printing an image file; (b) anon-printing drop deflection apparatus creating a zone intersecting thedrop curtain provided by positive and negative air duct assemblies todirect those drops to the Coanda gutter, and (c) an ink return line tothe ink reservoir, and (4) a print controller that (a) controls theprinting drum speed and synchronizes the drum location in accord withthe data feed to the jetting module and also (b) transmits electricalsignals to the jetting module CMOS circuitry that renders a rasterprocessed image into pixel by pixel ink stream stimulation instructionsusing nozzle plate heater pulse patterns by optimized waveforms togenerate non-printing catch drops and printing drops of ink delivered atthe printing substrate surface pixel locations, as required.

The fluid system used a Micropump Inc. MICROPUMP® series GJ-N23DB380Agear pump to deliver the ink through a Pall Corp. Disposable FilterAssembly capsule filter, DFA4201ZU0045, containing 0.45 μm nominaleffective pore size ULTIPOR® GF-HV glass fiber media at about 65 psid(0.45 MPa) pressure drop at the nozzle plate, which generated a uniformdrop velocity of about 20 m/s. The fluid system gear pump speed settingwas continually adjusted to provide and maintain constant fluid pressureat the jetting module to uniformly produce the desired drop velocity asper the system specification. The required system parameter settings forproper jetting and accurate ink replenishment were determined andrecorded to a computer file termed an “inkdex” to enable printing onother systems, such as a web press fitted two-up with production KODAK®PROSPER S10 Imprinting Systems. The deflected non-printing ink dropswere caught on a Coanda gutter and returned to the fluid system ink tankunder vacuum. Sustained operation of the printer in catch mode of thenon-printing drops resulted in gradual evaporation of the aqueous inksolvent vehicle. Ink concentration was maintained to within about 5% ofthe original ink concentration by addition of the aqueous pigment-freeReplenisher Fluid to the ink, if the latter became more than about 5%concentrated based on an ink electrical resistivity determination. Testtargets were raster image processed to produce digital printing signalinstructions for each pixel location at the appropriate transport speedof the test substrate at 600×600 pixels per inch (ppi) (236×236 pixelsper centimeter (ppcm)) addressability for speeds up to about 1,000 FPM.NewPage STERLING® Ultra Gloss paper and/or an uncoated, untreated freesheet paper (for example, International Paper 20-lb (75 g/m²) DATASPEED®Laser MOCR) was loaded on to the constant speed, rotating drum, whichwas synchronized with the print data controller. Various test imageswere printed at different substrate transport speeds that profiledsystem functional printing speed capability using a 600-nozzles per inchPROSPER Press Jetting Module in a near-production print-head assemblyconfiguration, which produced a 4.25-inch (10.8 cm) jet curtain printswath. Operational stability and start-up robustness (“runnability”)were also probed by printing into a catch pan and assessingtime-dependent jet straightness and print raggedness for extendedperiods, and by conducting multiple shut-down and start-up sequences toassess the time to achieve the first acceptable print and any requiredinterventions [service clean (cross-flush with ink), duct clean (flushwith storage fluid), and nozzle plate wipe]. Aqueous inkjet inkcomposition C-C (E) was found to be runnable and was loaded onto atwo-up web press fitted with production KODAK PROSPER S10 ImprintingSystems for long-term testing.

The present invention has been demonstrated above for use in acontinuous ink jet printer system that employs a gas flow dropdeflection mechanism, thermal drop stimulation devices, and nozzleplates fabricated out of silicon. However, the present invention canalso be employed in continuous ink jet printer systems that useelectrostatic drop deflection mechanisms, pressure modulation orvibrating body stimulation devices, and nozzles plates fabricated out ofother types of materials. Electrostatic deflection can be of the typethat includes separate drop charging and drop deflection electrodes orcan be of the type that incorporates both functions in a singleelectrode.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be obtained within the spirit and scopeof the invention.

1. An aqueous inkjet ink composition having a dynamic viscosity of lessthan or equal to 5 centipoise (5 mPa-sec) at 25° C., and consistingessentially of: (a) one or more polymer-dispersed pigment colorants in atotal amount of at least 0.9 weight % and up to and including 6 weight%, based on the total weight of the aqueous inkjet ink composition; (b)a composition consisting of one or more compounds represented by thefollowing Structure (I):HO—CH₂—CH₂—R   (I) wherein R is a substituted or unsubstituted phenylgroup or a substituted or unsubstituted phenoxy group, in a total amountof at least 0.5 weight % and up to and including 2 weight %, based onthe total weight of the aqueous inkjet ink composition; (c) one or morecompounds selected from water-soluble humectants, co-solvents, and bothwater-soluble humectants and co-solvents, in an amount of less than orequal to 20 weight %, based on the total weight of the aqueous inkjetcomposition, wherein each of the one or more polymer-dispersed pigmentcolorants has a 50^(th) percentile particle diameter of less than 70 nmand a 95^(th) percentile particle diameter of less than 150 nm, allparticle diameters being measured using a dynamic light scatteringparticle size analyzer.
 2. The aqueous inkjet ink composition of claim1, further comprising a (d) supplemental antimicrobial agent that isdifferent from the (b) composition.
 3. The aqueous inkjet inkcomposition of claim 2, wherein the (d) supplemental antimicrobial agentis iodopropynyl butyl carbamate, piroctone olamine, 2,4-dichlorobenzylalcohol, boric acid or a metal ion salt derived from boric acid, or acombination these compounds.
 4. The aqueous inkjet ink composition ofclaim 1, wherein the one or more (c) compounds are present in an amountof least 0.5 weight % and up to and including 15 weight %, based on thetotal weight of the aqueous inkjet ink composition.
 5. The aqueousinkjet ink composition of claim 1, further containing an anionicpolyurethane, an anionic non-aromatic acrylic polymer, an anionicstyrene-acrylic polymer, or a combination of two or more of suchmaterials, each of these materials having an acid number of at least 50.6. The aqueous inkjet ink composition of claim 1, wherein each of theone or more polymer-dispersed pigment colorants has a 50^(th) percentileparticle diameter of less than 60 nm and a 95^(th) percentile particlediameter of less than 110 nm, all particle diameters being measuredusing a dynamic laser light scattering particle size analyzer.
 7. Theaqueous inkjet ink composition of claim 1 having a pH of at least 7.5and up to and including
 11. 8. The aqueous inkjet ink composition ofclaim 1, further containing one or more promoters for the one or moreStructure (I) compounds in the (b) composition, each of which promoteris an alkane diol having a least 7 carbon atoms and up to and including12 carbon atoms, in an amount of less than or equal to 1.5 weight %,based on the total weight of the aqueous inkjet ink composition.
 9. Theaqueous inkjet ink composition of claim 8, wherein the promoter is1,2-octanediol.
 10. The aqueous inkjet ink composition of claim 1,wherein R is either an unsubstituted phenyl group or an unsubstitutedphenoxy group.
 11. An ink set comprising two or more aqueous inkjet inkcompositions, each of which independently has a dynamic viscosity ofless than or equal to 5 centipoise (5 mPa-sec) at 25° C., and each ofwhich aqueous inkjet ink compositions independently consists essentiallyof: (a) one or more polymer-dispersed pigment colorants in a totalamount of at least 0.9 weight % and up to and including 6 weight %,based on the total weight of the aqueous inkjet ink composition; (b) acomposition consisting of one or more compounds represented by thefollowing Structure (I):HO—CH₂—CH₂—R   (I) wherein R is a substituted or unsubstituted phenylgroup or a substituted or unsubstituted phenoxy group, in a total amountof at least 0.5 weight % and up to and including 2 weight %, based onthe total weight of the aqueous inkjet ink composition; (c) one or morecompounds selected from water-soluble humectants, co-solvents, and acombination of water-soluble humectants and co-solvents, in an amount ofless than or equal to 20 weight %, based on the total weight of theaqueous inkjet composition, wherein each of the one or morepolymer-dispersed pigment colorants has a 50^(th) percentile particlediameter of less than or equal to 70 nm and a 95^(th) percentileparticle diameter of less than or equal to 150 nm, all particlediameters being measured using a dynamic light scattering particle sizeanalyzer.
 12. The ink set of claim 11, comprising two or more of thefollowing: (i) an aqueous inkjet ink composition comprising apolymer-dispersed cyan pigment colorant, (ii) an aqueous inkjet inkcomposition comprising a polymer-dispersed magenta pigment colorant,(iii) an aqueous inkjet ink composition comprising a polymer-dispersedyellow pigment colorant, and (iv) an aqueous inkjet ink compositioncomprising a polymer-dispersed black pigment colorant.
 13. The ink setof claim 11, further comprising a particle-free colorless inkjetcomposition.
 14. The ink set of claim 13, wherein the particle-freecolorless inkjet composition comprises the same or different (b)composition as is present in each of the two or more aqueous inkjet inkcompositions.
 15. The ink set of claim 11, wherein any of the two ormore aqueous inkjet ink compositions further contains a (d) supplementalantimicrobial agent that is different from the (b) composition.
 16. Theink set of claim 15, wherein the (d) supplemental antimicrobial agent isiodopropynyl butyl carbamate, piroctone olamine, 2,4-dichlorobenzylalcohol, boric acid or metal ion salt derived from boric acid, or acombination of these compounds.
 17. The ink set of claim 11, whereineach of the one or more polymer-dispersed pigment colorants has a50^(th) percentile particle diameter of less than 60 nm and a 95^(th)percentile particle diameter of less than 110 nm, all particle diametersbeing measured using a dynamic laser light scattering particle sizeanalyzer.
 18. The ink set of claim 11, wherein any of the two or moreaqueous inkjet ink compositions further contains one or more promotersfor the one or more Structure (I) compounds of the (b) composition, eachof which promoters is an alkane diol having a least 7 carbon atoms andup to and including 12 carbon atoms, in an amount of less than or equalto 1.5 weight %, based on the total weight of the aqueous inkjet inkcomposition.
 19. The ink set of claim 18 wherein the promoter is1,2-octanediol.
 20. The ink set of claim 11, wherein R is either anunsubstituted phenyl group or an unsubstituted phenoxy group.